My honors Algebra teacher can't teach anything...

What percent of 75 is 15?

Translates to:

\(75\,*\,x\,=15\\ x\%=\frac{15}{75}\\ x=0.2\\ 0.2 = 20\% \)

Tips:

I'll use the same numbers for each example. 

Three variants

What percent of 100 is 40?

oldnum * {percent} = newnum

(What percent of the original number [100] gives you the new number [40]?)

100 * ? = 40

? = 40/100

? = 0.4

0.4 --> 40%

What is 40% of 100?

oldnum * percent = {newnum}

([40] percent of the original number [100] results in what number?)

100 * 40% = ?

40% --> 0.4

100 * 0.4 = 40

40% of what is 40?

{oldnum} * percent = newnum

([40] percent of what number gives you the new number [40])?

? * 40% = 40 

40% --> 0.4

? * 0.4 = 40

? = 40/0.4

? = 100

*this was hard for me at first, but with practice, you'll get used to the wording of the questions

If you are an honours student and you do not already know how to find the percentage of a number then I think you need to drop down several levels and study introductory arithmetic instead.  

15/75  *  100% = 20%