If John has three times as many marbles as Sarah and Sarah has 4 marbles, how many does John have?

To find out how many marbles John has, start with the information that Sarah has 4 marbles. Since John has three times as many marbles as Sarah, you can calculate John's total by multiplying the number of marbles Sarah has by 3.

So, you take Sarah's 4 marbles and multiply it by 3:

4 marbles (Sarah) × 3 = 12 marbles (John).

This means John has 12 marbles, which corresponds to the answer C. Therefore, the correct answer is confirmed through basic multiplication that illustrates the relationship established in the problem.