In this question there is 1 equation with 1 unknown variable. So it is absolutely possible to find the value of the unknown variable "x".
(4x - 1)/3 = 7/1
4x -1 = 7 * 3
4x - 1 = 21
4x = 21 + 1
4x = 22
x = 22/4
= 11/2
So the value of the unknown variable x is 11/2. So the correct option is option "d". Hope i have answered your question correctly and helped you to understand the method by which these problems should be done.
Answer:
Max vol = 2 cubic metres
Step-by-step explanation:
Given that from a square piece of cardboard paper of area size 9 m2 , squares of the same size are cut off from each corner of the paper.
Side of the square = 3m
If squares are to be cut from the corners of the cardboard we have the dimensions of the box as
3-2x, 3-2x and x.
Hence x can never be greater than or equal to 1.5
V(x) = Volume = 
We use derivative test to find the maxima

Equate I derivative to 0

If x= 3/2 box will have 0 volume
So this is ignored
V"(1/2) <0
So maximum when x =1/2
Maximum volume
=
cubic metres
The equation is the form:
Height = Constant / Width
There are several points that can be used to determine the constant. Picking out one which is (4,20)
20 = Constant / 4
Constant = 4(20)
Constant = 80
The constant is 80.