HELPP PLEASE!!!!!!
(Will give 15 points for right Answer)!!!!

Answer:
12
Step-by-step explanation:
The parallel sides must be the same length.
2x-6 = x+3
2x-x-6-3 = 0
x - 9 = 0
x = 9
x + 3 and 2x - 6 are both 12