21 is 55% of what number

You may use is/of method

21/x = 55/100

this is how you would model this problem. now, multiply both sides by 100.

so 2100/x = 55. multiply both sides by x.

so 2100=55x

divide both sides by 55. so

x is 38.18181818 (18 repeating forever) so the number they are asking for is that 38.18 (18repeating forever). round as necessary