Convert 300% into decimals. So move the decimal point 2 times to the left and you get 3.00 and multiply it by 5 and square it because area of square is s^2
$12,500 x 5% = $625.
$12,500 + $625 = $13,125.
Yes- though we may say "When will we ever use this?" ever so often in class, the reality is that we use mathematics in everyday life. From simple addition, to factoring, to finding the angles of various components to a building, math is always being used in real life.
I believe this is the distributive property.