Solve for a
a = \frac{220}{7} = 31\frac{3}{7} \approx 31.428571429
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9a-120-2a=100
Subtract 2a from both sides.
7a-120=100
Combine 9a and -2a to get 7a.
7a=100+120
Add 120 to both sides.
7a=220
Add 100 and 120 to get 220.
a=\frac{220}{7}
Divide both sides by 7.
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