Minimize $p = 6 a + 4 b$ Subject to the Following Constraints

Multiple Choice

Minimize $p = 6 a + 4 b$ subject to the following constraints.
$\begin{array} { l } a + b \geq 10 \\6 a + b \geq 30 \\a \geq 0 , b \geq 0\end{array}$

A) $a = 4$ , $b = 6$ , $p = 48$
B) $a = 10$ , $b = 0$ , $p = 60$
C) $a = 0$ , $b = 30$ , $p = 180$
D) $a = 0$ , $b = 10$ , $p = 40$
E) $a = 6$ , $b = 6$ , $p = 60$