Answer:
Step-by-step explanation:
90/100 * x = 15750
0.9 x = 15750
x = 15750/0.9
x = 17500
Now check this by taking 10% off. Do you get 15750?
Let's see
10/100 of 17500 = 1750
Subtract that from 17500
17500 - 1750 = 15750 which is exactly what you should get.
The question is worded a bit strangely (in my opinion anyway), but I think your teacher wants you to describe how exponents work.
Let's say we had the expression 
The base is 5 as its the bottom most value (think of something like the base of a tree or building). The exponent is 3.
The exponent of 3 tells the reader to multiply the base 5 by itself 3 times like so

With larger exponents, it becomes more tedious to write out all the repeated multiplications, which is why many calculators have an exponent button to save time.
Step-by-step explanation:
One hundred minus five n