Keisha wants to read for 90 minutes. so far , she has read 30% of her goal. how much longer does she need to reach her goal?

30% of 90            whenever it says "of" put in a multiplication sign 
30% x 90              take out the % sign (percent means divided by 100)
30/100 =3/10               simplify,then multiply by 90
3/10 x 90 = 270/10          simplify
270 = 27     
90 - 27 = 63            subtract 27 because it is the amount read so far from the total
Keisha has to read 63 more minutes to reach her goal.