The two bases added together divided by two should equal the mid segment which is 25. Plugging in the equation. You have (3x + 2) + (7x - 2) divided by 2. 7x + 3x = 10x. Then 2-2 cancel each other out. 10x/2 = 5x. 5x = 25. When you simplify it you get x = 5.