QR is the median of the trapezoid, so its length is the average of the top and bottom bases. Write that. Say (length of QR)=1/2 of (length of the top + length of the bottom). That gives you a nice simple equation that you can easily solve for 'x'.
Step-by-step explanation:
refer the above attachment
2) would be equal to 19! / 2^9 * 9!