Answer:
more than you can afford is a correct sentence with good meaning
You know that the sum of a and b is 24, because the average is the sum of the numbers divided by the amount of numbers added together, and 12*2 is 24. Add 3 to 24 so you have 27, and then divide that by 3 because there are now 3 numbers in the set. The average of a, b, and c is 9.
