Solve for b
b=30
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390=\left(1\times 10+3\right)b
Multiply both sides of the equation by 10.
390=\left(10+3\right)b
Multiply 1 and 10 to get 10.
390=13b
Add 10 and 3 to get 13.
13b=390
Swap sides so that all variable terms are on the left hand side.
b=\frac{390}{13}
Divide both sides by 13.
b=30
Divide 390 by 13 to get 30.
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