If you would like to solve the system of equations 3r - 4s = 0 and 2r + 5s = 23, you can do this using the following steps:
3r - 4s = 0 /*5
2r + 5s = 23 /*4
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15r - 20s = 0
8r + 20s = 92
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15r - 20s + 8r + 20s = 0 + 92
23r = 92
r = 92/23
r = 4
3r - 4s = 0
3 * 4 - 4s = 0
12 - 4s = 0
4s = 12
s = 12/4
s = 3
(r, s) = (4, 3)
The correct result would be b. r = 4, s = 3.
