To solve for \( c \) in the equation \( 8c - 3c = 15 \), first simplify the left side:
\[ 8c - 3c = 5c \]
Now the equation is:
\[ 5c = 15 \]
Next, divide both sides by 5:
\[ c = \frac{15}{5} \]
Simplifying gives:
\[ c = 3 \]
So, the solution is:
\[ c = 3 \]