Chapter 2 - Linear and Quadratic Functions - Section 2.3 Quadratic Functions and Their Zeros - 2.3 Assess Your Understanding - Page 146: 19

the zeros are $x=-4$ or $x=4$ and the $x$-intercepts are $(-4,0)$ and $(4,0)$.

By factorization, we have $$ P(x)=3x^2-48=3(x^2-16)=3(x+4)(x-4) .$$ That is, we have $x+4=0 $ or $x-4=0$. So the zeros are $x=-4$ or $x=4$ and the $x$-intercepts are $(-4,0)$ and $(4,0)$.