Question

How many carbon atoms are in four molecules of glucose, or 4C6 H12 O6?

Answer 1

4 x 6 = 24 because of the coefficient 4 and the subscript 6

Answer 2

It gives you the answer! The 6 after the C (carbon) tells you how many of that element there are in the molecule. So 6 is your answer!
Hope this  helps :)