You have the following information:
- CG = 2x + 7
- CD = 74
- EF bisects CD
In order to find the value of x, you consider that:
CG + GD = CD
If EF bisects CD, then CG = GD = 2x + 7.
You replace the given expressions for CG and CD in the previous equation, and solve for x, just as follow:
CG + GD = CD
2x+7 + 2x+7 = 74 simplify like terms
4x + 14 = 74 subtract 14 both sides
4x = 74 - 14
4x = 60 divide by 4 both sides
x = 60/4
x = 15
Hence, the value of x is x = 15
