Melody

inverse tan is the same as arc tan.

[2nd][atan] number

$$\\(16y^6)^{1/2}\\
=\sqrt{16y^6}\\
=\sqrt{16}*\sqrt{y^6}\\
=4y^3$$

First the surface are must be in square units.    

l*b*h=750   (1)

2(lb+lh+bh)=2600

lb+lh+bh=1300

I do not think that you can solve this because 3 unknowns usually needs 3 equations to solve.

$$\underset{\,\,\,\,{\textcolor[rgb]{0.66,0.66,0.66}{\rightarrow {\mathtt{lbh, lb, lh, bh}}}}}{{solve}}{\left(\begin{array}{l}{\mathtt{Lbh}}={\mathtt{750}}\\
{\mathtt{Lb}}{\mathtt{\,\small\textbf+\,}}{\mathtt{Lh}}{\mathtt{\,\small\textbf+\,}}{\mathtt{bh}}={\mathtt{1\,300}}\end{array}\right)} \Rightarrow \left\{ \begin{array}{l}{\mathtt{lbh}} = {\mathtt{750}}\\
{\mathtt{lb}} = {\mathtt{\,-\,}}{\mathtt{r20}}{\mathtt{\,-\,}}{\mathtt{r19}}{\mathtt{\,\small\textbf+\,}}{\mathtt{1\,300}}\\
{\mathtt{lh}} = {\mathtt{r20}}\\
{\mathtt{bh}} = {\mathtt{r19}}\\
\end{array} \right\}$$

I have no idea what thid calculator has done   

The meaning of this question is not clear at all  

$$\\5.00*10^{-4}t^2+0.20t+40=30\\\\
\frac{5}{10^{4}}t^2+0.20t+40=30\\\\
t^2+0.04*10^{4}t+8*10^{4}=6*10^{4}\\\\
t^2+400t+80000=60000\\\\
t^2+400t+20000=0\\\\$$

$${{\mathtt{t}}}^{{\mathtt{2}}}{\mathtt{\,\small\textbf+\,}}{\mathtt{400}}{\mathtt{\,\times\,}}{\mathtt{t}}{\mathtt{\,\small\textbf+\,}}{\mathtt{20\,000}} = {\mathtt{0}} \Rightarrow \left\{ \begin{array}{l}{\mathtt{t}} = {\mathtt{\,-\,}}{\mathtt{25}}{\mathtt{\,\times\,}}{{\mathtt{2}}}^{\left({\frac{{\mathtt{5}}}{{\mathtt{2}}}}\right)}{\mathtt{\,-\,}}{\mathtt{200}}\\
{\mathtt{t}} = {\mathtt{25}}{\mathtt{\,\times\,}}{{\mathtt{2}}}^{\left({\frac{{\mathtt{5}}}{{\mathtt{2}}}}\right)}{\mathtt{\,-\,}}{\mathtt{200}}\\
\end{array} \right\} \Rightarrow \left\{ \begin{array}{l}{\mathtt{t}} = -{\mathtt{341.421\: \!356\: \!237\: \!309\: \!504\: \!9}}\\
{\mathtt{t}} = -{\mathtt{58.578\: \!643\: \!762\: \!690\: \!495\: \!1}}\\
\end{array} \right\}$$

If sin(theta)=3/5 and tan is less than theta, what is the value of sec(2theta)

I have no idea what "tan is less than theta" even  means 

BUT

  $$\\If\qquad sin\theta=\frac{3}{5}=0.6 \qquad then \qquad cos\theta=\pm \frac{4}{5}=0.8\\\\
sec2\theta \\\\
= \frac{1}{cos2\theta}\\\\
= \frac{1}{cos^2\theta - sin^2 \theta}\\\\
= \frac{1}{0.64 - 0.36}\\\\
= \frac{1}{0.28}\\\\
= \frac{100}{28}\\\\$$

$${\frac{{\mathtt{100}}}{{\mathtt{28}}}} = {\frac{{\mathtt{25}}}{{\mathtt{7}}}} = {\mathtt{3.571\: \!428\: \!571\: \!428\: \!571\: \!4}}$$

Yes you answered first Titanium but your answer was wrong!

Nice answer DarkBlaze347    

$$0.2 \div 240$$

$${\frac{{\mathtt{0.2}}}{{\mathtt{240}}}} = {\frac{{\mathtt{1}}}{{\mathtt{1\,200}}}} = {\mathtt{0.000\: \!833\: \!333\: \!333\: \!333\: \!3}}$$

Here are some ideas that I just copied from our "reference Material " sticky topic       

HOMEWORK SITES 

Review on Mathopolis homework site

Yes I used to be like that but I spend so much time socializing with people in different time zones that I  usually finish for the day quite late.  

BUT

1 am is still pretty late.   

Yah, our hotel business will be booming!