Solve for a
a=72
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a=4\left(90-a\right)
Multiply both sides of the equation by 12, the least common multiple of 12,3.
a=360-4a
Use the distributive property to multiply 4 by 90-a.
a+4a=360
Add 4a to both sides.
5a=360
Combine a and 4a to get 5a.
a=\frac{360}{5}
Divide both sides by 5.
a=72
Divide 360 by 5 to get 72.
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