Final answer:
Mark requires training 15 clients to make $2,500, given that he makes $500 for every 3 clients. Since the answer of 15 clients is not among the provided options, there appears to be an error in the question's choices.
Step-by-step explanation:
The question asks how many clients Mark needs to train to save $2,500, knowing that he makes $500 for every 3 clients. To find the answer, we need to determine how many sets of 3 clients would earn Mark $2,500.
First, we calculate how many times $500 goes into $2,500:
$2,500 / $500 = 5
Now, since each set of 3 clients gives him $500, we multiply the number of sets by 3
$2,500 / $500 = 5
5 sets × 3 clients/set = 15 clients
Therefore, Mark needs 15 clients to make $2,500. This is not one of the provided options (a) 3 clients, (b) 6 clients, (c) 9 clients, or (d) 12 clients. It seems there might be a mistake in the options provided.