Answer:
 c) 5(1/2 + x) 
Explanation:
You want the expression that represents "5 multiplied by the sum of 1/2 and x."
Product
The wording of the statement tells you it will have the form of a product:
 5×sum . . . . . . . . 5 multiplied by a sum
That eliminates all of the answer choices except C.
Sum
The wording tells you the sum is of 1/2 and x, so it is represented by ...
 1/2 +x . . . . . . . . . sum of 1/2 and x
Expression
Using the sum expression in the above product expression, we have ...
 5(1/2 +x)