Answer:
x/100 x 30 = 21 (solve for x) x =70
I wish I could explain more but if your just lazy to do this i wont explain but if you honestly dont know I will explain, so solve for x you must multiply by a 100 on both sides and on the right side you multiply it to the fraction so x/100 x 100 = x (variable by itself means 1) then 21 x 100 = 21,000 therefore you are left with 30x since you are multiplying x and 30 together then you will divide by 30 on both sides to get x = 70