Question 485875
The lines are perpendicular, so angle PQR is 90 degrees.
Therefore, set an equation 4 + 7a + 9 + 4a = 90 degrees.
13 + 11a = 90 degrees.
11a = 77 degrees.
a = 7 degrees.
7 * 7 = 49 + 4 = 53
7 * 4 = 28 + 9 = 37 
37 + 53 = 90.
Cleomenius.