I got it! The answer is 9!
How I did it:
First I plugged in x as 0, f(0) = 0 / -1 = 0
(0p + q)/(0r + 1) = f(5 * 0) = 0 => q/1 = 0 => q = 0
Next I plugged in x as -1, f(-1) = 1/2
(p/2 + 0)/(r/2 + 1) = f(-5) = 5/6
p/(r + 2) = 5/6
6p = 5r + 10 (1)
Next I plugged in x as -2, f(-2) = 2/3
(2p/3)/(2r/3 + 1) = f(-10) = 10/11
2p/(2r + 3) = 10/11
22p = 20r + 30
11p = 10r + 15 (2)
Take equation (1) and multiply by 2 => 12p = 10r + 20 (1b)
Take equation 1b - equation 2 => p = 5
Plug it back into equation 1 => 30 = 5r + 10 => r = 4
p + q + r = 5 + 0 + 4 = 9