Solve the Problem $\frac { x } { a } + \frac { y } { 5 } + \frac { z } { 6 } = 1$

Solve the problem.
-For what value of a is the volume of the tetrahedron formed by the coordinate planes and the plane $\frac { x } { a } + \frac { y } { 5 } + \frac { z } { 6 } = 1$ equal to 4 ?

A) $a = \frac { 4 } { 5 }$
B) $a = \frac { 8 } { 15 }$
C) $a = \frac { 16 } { 15 }$
D) $\mathrm { a } = \frac { 2 } { 5 }$