The side AB = BD
7x + 10 = 9x - 2
SImplify for x :
Subtract 7x from both side :
7x + 10 - 7x = 9x - 7x - 2
10 = 2x - 2
Add 2 on both side :
10 + 2 = 2x - 2 + 2
12 = 2x
divide both side by 2 :
2x/2 = 12/2
x = 6
