Answer: So Lucía has 3.5 hours left, and need 1/2 of an hour (or 0.5 hours) to do one oil change.
a) If you divide the total time she has by the time she needs for each oil change, then you got the total number of oil changes that she can do in that time; this is:
3.5/0.5 = 7
So she can do 7 oil changes in 3.5 hours.
b) If she can complete two car inspections in the same amount of time it takes her to complete one oil change, then she can do two car inspections in 0.5 hours.
2*car inspections = 0.5 hours
car inspection = (0.5/2) hours
then one car inspection will take 0.5/2 = 0.25 hours.
c) Two ways to solve this:
1) Do the same that we did in a), this is: 3.5/0.25 = 14
she can do 14 car inspections.
2) If in 3.5 hours, she can do 7 oil changes, and in the time she does an oil change, she can do two car inspections, then in 3.5 hours she can do 7*2 car inspections, and 7*2 = 14