Can someone please help me with this problem 36 is .75% of what number? I don't understand how do I get the answer.

Percent means out of 100, so 0.75% means 0.75/100 or 0.0075 so that there is a number, say x, for which 0.75% of x (0.0075x) is 36 (equals 36). This means 
0.0075x=36 
x=36/0.0075=4800 


:)