Use the substitution method to solve:
9c + 3s = 75
5c + 8s = 67
Check Format
Equation 1 is in the correct format.
Check Format
Equation 2 is in the correct format.
Rearrange Equation 2 to solve for c:
5c + 8s = 67
Subtract 8s from both sides to isolate c:
5c + 8s - 8s = 67 - 8s
5c = 67 - 8s
Now divide by 5:
| 5c | |
| 5 |
| = |
| 67 - 8s |
| 5 |
Revised Equation 2:
| c = | 67 - 8s |
| 5 |
Plug Revised Equation 2 value into c:
9(c) + 3s = 75
9 * ((67 - 8s)/5) + 3s = 75
((603 - 72s)/5) + 3s = 75
Multiply equation 1 through by 5
5 * (((603 - 72s)/5) + 3s = 75)
5 * (((603 - 72s)/5) + 3s = 75)
603 - 72s + 15s = 375
Group like terms:
-72s + 15s = 375 - 603
-57s = -228
Divide each side by -57
| -57s | |
| -57 |
| = |
| -228 |
| -57 |
| s = | -228 |
| -57 |
s = 4
Plug this answer into Equation 1
9c + 3(4) = 75
9c + 12 = 75
9c = 75 - 12
9c = 63
Divide each side by 9
| 9c | |
| 9 |
| = |
| 63 |
| 9 |
| c = | 63 |
| 9 |
c = 7
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