How to simplify numbers

Hopes this helps:

•ROUND IT OFF
Create zeros.
So 199 becomes 200.

•ROUND THE ORDER OF MAGNITUDE
Round a lot, to the nearest “power ten”.
So 218 comes 100, and 2,180 becomes 1,000.

•SLIDE THE DECIMAL POINT
Compact those zeros created by rounding.
So 200,000,000 becomes 2•10^8 (exponential notation).

•SUBSTITUTE A NUMBER YOU CAN REMEMBER
Instead of rounding, find a nearby number you can remember.
So 218 becomes 222, or 210 or 200, something else easy.

It would be 15 m how i got the answer: (20x20) + b^2 = (25x25)400 + b^2 = 625625-400=225square that and get 15hope this : )