Final answer:
Marcus' brother Craig has 5 toy cars, this is one-third of the number of toy cars that Marcus has.
Step-by-step explanation:
The question asks how many toy cars Marcus' brother Craig has if Marcus has 15 toy cars, and that is 3 times as many as Craig has. To find the answer, we need to divide the number of toy cars Marcus has by 3 since Craig has a third of what Marcus has.
We calculate 15 toy cars ÷ 3 = 5 toy cars. Therefore, Craig has 5 toy cars.