Solve by the elimination method:

Question

7r-9s=-35
9r+7s=85

Answer 1

(7r-9s)7=(-35) 7
(9r+7s)9=85.9
7(7r-9s)=765
7(7r-9s)=-35.7
9(9r+9s)=765
7(7r-9s)=-245
9.9r+9.7s=765
7.7r-7.9s=-245
81r+63s=765
49r-63s=-245
81r+63s=765
49r-63s=-245
(81r+63s)+(49r-63s)=765.245
49r-63s=-245
1230r=520
49r-63s=-245
130r/130=520/130
49r-63s=-245
r=2^3-1
49r-63s=-245
r=4
49.4-63s=-245
196-63s=-441
63s/63=441/63
s=7^2-1
s=7

Answer 2

No, no, no, no, no, no, no...I have no idea what all that nonsense above is.
7r-9s=-35
9r+7s=85
Multiply the first equation by 7 and the bottom by 9 so that the s's cancel.
49r-63s=-245
81r+63s= 765
130r=520
r=4
Now put r=4 back into any original equation.
9(4)+7s=85
36+7s=85
7s=49
s=7
(4,7)