Algebra
posted by Ashly .
Solve by the elimination method:
7r9s=35
9r+7s=85

(7r9s)7=(35) 7
(9r+7s)9=85.9
7(7r9s)=765
7(7r9s)=35.7
9(9r+9s)=765
7(7r9s)=245
9.9r+9.7s=765
7.7r7.9s=245
81r+63s=765
49r63s=245
81r+63s=765
49r63s=245
(81r+63s)+(49r63s)=765.245
49r63s=245
1230r=520
49r63s=245
130r/130=520/130
49r63s=245
r=2^31
49r63s=245
r=4
49.463s=245
19663s=441
63s/63=441/63
s=7^21
s=7 
No, no, no, no, no, no, no...I have no idea what all that nonsense above is.
7r9s=35
9r+7s=85
Multiply the first equation by 7 and the bottom by 9 so that the s's cancel.
49r63s=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)