Write an algebraic expression that models the word phrase. the product of 8 and the sum of a number x and 3

"Sum" means addition, so the sum of a number x and 3 is
x + 3

"Product" means multiplication, so the product of 8 and x + 3 is
8(x + 3)

You need the parentheses to show it's the product of 8 and x + 3.
If you wrote only 8x + 3, that would mean the product of 8 and x, then you add 3 to it, which is different from your problem.