To factor the expression \( 21q + 56 \), we start by finding the greatest common factor (GCF) of the coefficients 21 and 56.
- The factors of 21 are: \( 1, 3, 7, 21 \).
- The factors of 56 are: \( 1, 2, 4, 7, 8, 14, 28, 56 \).
The GCF of 21 and 56 is \( 7 \).
Next, we factor out the GCF from the expression:
\[ 21q + 56 = 7(3q) + 7(8) = 7(3q + 8) \]
Thus, the factored form of \( 21q + 56 \) is:
\[ \boxed{7(3q + 8)} \]