Alan

[A] = [A0]*e^(-k*t)

[A] = 0.7*e^(-0.0942*20)

I'll leave you to do the number crunching (you can just enter the right-hand side into the calculator on the home page here).

Have a look at:  http://www.piday.org/million/ 

If you insist on a formal numerical method here's one way of doing it:

but this is a very heavy-handed way to solve such a simple problem!

{Are you sure you don't mean log1.5?   Log1.5 → log(3/2) → log3 - log2 → q - p}

log1.25 → log(5/4) → log5 - log(2^2) → log(10/2) - 2log2 → log(10) - log2 - 2log2 → 1 - 3log2 → 1 - 3p.  (Assuming log is log to base 10).

Can also write 

a = log(4/3) → log4 - log3 → log(2^2) - log3 → 2log2 - log3

and

b = log(10/9) → log10 - log9 → 1 - log(3^2) → 1 - 2log3.  (I'm assuming log is log to base 10)

From these you should be able to rearrange to get log2 and log3 in terms of a and b.

Hmm.

One way is to find the length of each side using Pythagoras (length^2 = (ya - yb)^2 + (xa - xb)^2)

Then use Heron's formula:  Area = sqrt(s(s-a)(s-b)(s-c)), where a, b and c are the three side lengths and s is (a+b+c)/2

.

Search Desmos graph plotter

Let a be the shorter diagonal, then b = a + 2 and we have:

a(a+ 2)/2 = 40

or:    a^2 + 2a - 80 = 0

or:  (a + 10)(a - 8) = 0

The only positive solution is a = 8 m, so b = 10 m

Or, if you prefer, I replaced sqrt(x) by u and sqrt(y) by v, found the values of u an v (by inspection - i.e. guesswork!), then squared the resulting values to get x and y.