## Thinking Mathematically (6th Edition)

$x$; $6$
RECALL: $f(a)$ represents the value of the function $f$ when $x=a$. To find $f(6)$ in the given function, replace $x$ with $6$ to obtain: $f(x) = 3x+5 \\f(6) = 3(6) + 5 \\f(6) = 18+5 \\f(6) = 23$ Thus, the missing expressions in the given statement are: $x$; $6$