Question

5r-4s=8 4r+5s=31

Answer 1

5r-4s=8

4r+5s=31

25r - 20s = 40 (the first equation x5)
16r + 20s = 124 (the second equation x4)

41r = 164 (adding the last 2 equations)
r = 4

4s = 5r -8 = 20 -8 = 12
s = 3