To find \( f(4) \) using the function \( f(a) = 6(a + 1) - 7 \), we can substitute \( a = 4 \) into the function.
\[ f(4) = 6(4 + 1) - 7 \]
Now, simplify inside the parentheses:
\[ f(4) = 6(5) - 7 \]
Next, multiply:
\[ f(4) = 30 - 7 \]
Now, subtract:
\[ f(4) = 23 \]
So, the simplified answer is:
\[ \boxed{23} \]
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