Solve for a
a=\frac{13}{15}\approx 0.866666667
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21a-28-3\left(4a+5\right)-\left(6a+2\right)=a+8\left(4a-9\right)+1
Use the distributive property to multiply 7 by 3a-4.
21a-28-12a-15-\left(6a+2\right)=a+8\left(4a-9\right)+1
Use the distributive property to multiply -3 by 4a+5.
9a-28-15-\left(6a+2\right)=a+8\left(4a-9\right)+1
Combine 21a and -12a to get 9a.
9a-43-\left(6a+2\right)=a+8\left(4a-9\right)+1
Subtract 15 from -28 to get -43.
9a-43-6a-2=a+8\left(4a-9\right)+1
To find the opposite of 6a+2, find the opposite of each term.
3a-43-2=a+8\left(4a-9\right)+1
Combine 9a and -6a to get 3a.
3a-45=a+8\left(4a-9\right)+1
Subtract 2 from -43 to get -45.
3a-45=a+32a-72+1
Use the distributive property to multiply 8 by 4a-9.
3a-45=33a-72+1
Combine a and 32a to get 33a.
3a-45=33a-71
Add -72 and 1 to get -71.
3a-45-33a=-71
Subtract 33a from both sides.
-30a-45=-71
Combine 3a and -33a to get -30a.
-30a=-71+45
Add 45 to both sides.
-30a=-26
Add -71 and 45 to get -26.
a=\frac{-26}{-30}
Divide both sides by -30.
a=\frac{13}{15}
Reduce the fraction \frac{-26}{-30} to lowest terms by extracting and canceling out -2.
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