Linear proportion means you are able to graph a Straight Line by changing the AXIS from normal X/Y:
Remembering a straight line equation is
Y = mX + c
(So altering Y and X to make straight line)

Giving an example:

Part (A):
Y = 4x^2
Let Y-axis be Y (no change),
X- axis be x^2,
So when u plot Y against X^2:
Then ur graph will be "Y = 4X",
Which is a diagonal straight line
So the variables are
y and x^2

B) Y = 3 x^(0.5)
Variables are Y and x^0.5
(Graph will be Y = 3X)

C) y^2 = 5 x^3
Variables are y^2 and x^3
(Graph will be Y = 5X)

D) p^3 = q^2
Variables are p^3 and q^2
(Graph will be P = Q)