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Hi
Assume you meant:
2r - s = 10 Or 
rs - s^2 = 12
|Multiplying thru by 2 so as all denominators = 1
(s+10)s - 2s^2 = 24
s^2 + 10s - 2s^2 = 24
10s - s^2 = 24
s^2 - 10s + 24 = 0
factoring
(s-6)(s-4) = 0
(s-6) = 0 , s = 6 and r = 8
0r (s-4) = 0 , s = 4 and r = 7