To determine if \( c = 5 \) is a solution to the equation \( 21 = 5c \), we can substitute \( c \) with \( 5 \) in the equation:
\[ 21 = 5(5) \] \[ 21 = 25 \]
Since \( 21 \) does not equal \( 25 \), \( c = 5 \) is not a solution to the equation \( 21 = 5c \).
To find the actual solution, we can solve for \( c \):
\[ 21 = 5c \] \[ c = \frac{21}{5} \] \[ c = 4.2 \]
So, the solution to the equation \( 21 = 5c \) is \( c = 4.2 \).