Question

Quadrilateral RSTU is a parallelogram. What must be the value of x?

Answer 1

Well, that's pretty easy. The main thing you need to know to solve this task is that since the opposite sides of a parallelogram are congruent,sides RS = TU. 
Then we can find the value of x : 
$2x+5 = x + 16. x = 11$
I am sure that helps!