Answer:
The dimensions are height=4 inches, width=8 inches and lenght=12 inches.
Explanation:
The volumen of a box is:

we don't know the width so let's assume it as x.

that gives us a cuadratic equation:

let's rerrangage it:
∞

we can obtain the value of x using the quadratic formula:

that formula gave us two results:

we have to take te possitive number, so the width is 8 inches and the length is 8+4=12 inches
height=4 inches
width=8 inches
lenght=12 inches
Volume=4*8*12=384 cubic inches.