Question

Write an equation and solve. 21 is 35% of what number?

Answer 1

It's 35% of 60. You can create a ratio. I included the ratio but you can easily substitute 60 with the variable x.
(21/60)=(35/100)

Answer 2

21 is 35% of 60.
35% * x = 21
Multiply both side by 100 and divide both sides by 35.
x = 21 * 100/35
21 * 100 = 2100
2100/35 = 60.