Consider the question. Five coaster vans are used to transport students for their field trip. Each van carries 28 students, 60 of which are boys. How many are girls?
 If the answer is '80'; explain the reasoning:
There are a total of 5 vans x 28 students = 140 students. If 60 are boys, then 140 - 60 = 80 of these students are girls.