2 times the length of the midsegment equals the length of the base. That being said, your equation will be 2(x+21)=x+32.
First, use the distributive property on 2(x+21). You are left with 2x+42=x+32.
Subtract x from both sides. You are left with x+42=32.
Finally, subtract 42 from both sides of the equation. You are left with your answer: x=-10.
Check your work: -10+21=11 and -10+32=22
11 is half of 22.
