Answer:
5(x-3)
Explanation:
The word "SUM" means the answer to an "ADDITION". 
"SUM" is always used with the word "AND" to indicate which numbers are being added. 
The SUM of a number AND -3 is written as: 
( x + ( − 3 ) ), or ( x -3 ) 
(where we have chosen the number to be x .) 
But we want FIVE of those sums; this means: 
5 ( x − 3 )