13а-4-21а-7

To simplify the expression \( 13a - 4 - 21a - 7 \), you should combine like terms.

1. Combine the \( a \) terms: \[ 13a - 21a = -8a \]

2. Combine the constant terms: \[ -4 - 7 = -11 \]

Putting it all together, the simplified expression is: \[ -8a - 11 \]