
Andrew N. answered 07/31/19
SAT Insider: Let Me Reveal My Secrets
The keyword in the question is sum, which indicates that we need to add. The SAT does drop in these operational terms sometimes, so it is worth knowing the following:
sum means add or plus
difference means subtract or minus
product means multiply or times
quotient means divide or divided by
Here, we are asked for the sum of 4 and 5, and, in keeping with your request, that means that we are looking to interpret four plus five, which equals nine.
Good luck with your studies.