Question

The height of a box is 3 inches. The length is three inches more than the width. Find the width if the volume is 390. Select one: A. 13 in. B. 130 in. C. 10 in. D. 3 in.

Answer 1

let
x---------> the length side of the box
y---------> the width side of the box

we know that
h=3 in
V=390 in³
volume of the box=x*y*3-------> 390=x*y*3-----> x*y=130------> equation 1
x=3+y------> equation 2

substitute 2 in 1
[3+y]*y=130-----> y²+3y=130------> y²+3y-130=0

using a graph tool------> to resolve the second order equation
see the attached figure

the solution is
y=10 in
x=3+y-----> x=3+10-----> x=13 in

the answer is
the width is 10 in