# How do you evaluate the function f(x) = 3x+7 for f(-5)?

$f \left(5\right) = 22$.
To evaluate a function in a specific point, you just need to substitute every occurrence of $x$ with that specific value.
In fact, $f \left(x\right) = 3 x + 7$ means "take a number $x$, triple it, and then add five". So, if our number is $5$, we must compute three times $5$ and then add seven, which is exactly what happens if we do the substitution:
$f \left(5\right) = 3 \cdot 5 + 7 = 15 + 7 = 22$