Congruent means they are the same length.
Set both lines equal to each other and solve for x:
x + 5 = 2x -10
Subtract x from both sides:
5 = x -10
Add 10 to both sides:
x = 15
Now you have a value for x, replace x in the equation of the line and solve:
QR = x +5 = 15 +5 = 20