The school band earned $10 / family * 3 families = $30 from three families. The school band earned $15 / family * 5 families = $75 from 15 families. The school band earned $30 + $75 = $105 total. The school band needs $150 - $105 = $45 more to reach their goal.
This justifies what answer for what question? Q & A:
The school band is having a car wash to raise money. Their goal is to collect $150. So far they have earned $10 each from three families and $5 each from 15 families. How much more money do they have to earn to reach their goal?
45