Use the Two-Stage Method to Solve $x_{1} \geq 0$ And $x_{2} \geq 0$

Multiple Choice

Use the two-stage method to solve.
-Find $x_{1} \geq 0$ and $x_{2} \geq 0$ such that
$$\begin{aligned}& 3 x_{1}+4 x_{2} \geq 48 \\& 3 x_{1}+4 x_{2} \leq 60\end{aligned}$$
And $\mathrm{z}=6 \mathrm{x}_{1}+7 \mathrm{x}_{2}$ is maximized.

A) $x_{1}=6, x_{2}=12, z=120$
B) $x_{1}=20, x_{2}=5, z=155$
C) $x_{2}=15, x_{1}=0, z=105$
D) $x_{1}=20, x_{2}=0, z=120$