To factor the expression \( 20c + 15d \), we first identify the greatest common factor (GCF) of the coefficients 20 and 15.
The GCF of 20 and 15 is 5. Now, we can factor out 5 from both terms:
\[ 20c + 15d = 5(4c + 3d) \]
Thus, the factored form of the expression is:
\[ 5(4c + 3d) \]
Here, \( 5 \) is a whole number greater than 1.