8b+12b-21+b

To simplify the expression \(8b + 12b - 21 + b\), you combine the like terms (the terms with \(b\)):

1. Combine \(8b\), \(12b\), and \(b\): \[ 8b + 12b + b = (8 + 12 + 1)b = 21b \]

2. Now, include the constant term \(-21\): \[ 21b - 21 \]

So, the simplified expression is: \[ 21b - 21 \]