To find the number of trucks the mechanic worked on, we can subtract the number of cars from the total number of vehicles worked on:
Total vehicles = 18 Cars worked on = 13
Trucks worked on = Total vehicles - Cars worked on = 18 - 13 = 5
Now we can find the ratio of cars to trucks:
Cars : Trucks = 13 : 5
Thus, the ratio of cars to trucks that were worked on for the week is 13:5.
So, the correct response is: 13:5 (ratio of 13 to 5).