A bisected line would be the midpoint, so point E is the middle of DG
This means DE is 1/2 of DG
2z + 2 = 1/2(5z-7)
2z + 2 = 2.5z -3.5
Add 3.5 to both sides
2z + 5.5 = 2.5z
Subtract 2z from both sides
5.5 = 0.5z
Divide both sides by 0.5
Z = 11
Now replace z with 11 and solve for DG
5(11)-7 = 55-7 = 48
DG = 48
