The answer is 1/2(10 + x).
The sum is the result after addition and to get the half of any value you can multiply it by 1/2.
For instance,
2 + 2 = 4.
4 is the sum
4 * 1/2 = 4/2 = 2
4 is essentially half of what is used to be.
Now that we know this,
(10 + x)
We can take half of that quantity. So our new expression looks like: 1/2(10 + x)
