Precalculus: Concepts Through Functions, A Unit Circle Approach to Trigonometry (3rd Edition)

$-\frac{7}{3}$ is the zero of $f(x)$.
Set $f(x)=0$ then solve for $x$: $0=3 x+7$ Adding $-7$ on both sides we get $-7 = 3x$ Divide by $3$ on both sides: $x=-7 / 3$. Thus, the zero of $f(x)$ is $-\frac{7}{3}$.