Answer:
x=18
Step-by-step explanation:
Because of the SSS criterion, The congruent sides are equal to each other. Meaning, Side AB is congruent to side AD. With this, you can set side BC and side DC equal to each other to solve for x.
x+12=2x-6
You subtract x to both sides;
12=x-6
You then add 6 to both sides to get x alone.
18=x or x=18.
