The sum of 8 and 5 is equal to the difference of a number and 7

8+5 = x - 7

Explanation:

a number is X

sum means addition

difference means subtraction

To solve: You need to isolate x on one side of the equation (one side of the = sign). To do this, add 7 to both sides so you can move it from one side to the other:

8 + 5 = x - 7

+7 + 7

As you can see, adding 7 will cancel out the - 7 on the right side, and move it to the left. Now the equation you are left with is

8 + 5 + 7 = x

Finally add the numbers together and you will get your value for x.

8 + 5 + 7 = 20

20 = x