The diagram is asking for you to find out what 1/3 of the missing number is, and it shows that 3/5 + 1/2 is equal to a third of the whole. So, you would multiply 3/5 and 1/2 by 3, and make sure to have the parentheses because you want to multiply the <u>sum</u> of 3/5 and 1/2 by 3.
