Thanks Mr Eric :)
I have also derived the same answer but the answer key says the answer should be y = 1/3x + 5/6. Another tutor, Mr Muhammad has also advised me the same answer as us. Now I seriously think that the answer sheet could be wrong.

Candice, let’s see what happens when we put x^2 as the vertical axis and xy as the horizontal axis for a change instead.

Gradient: 1/3
Horizontal (xy) - axis: 6

Y = mX + c
Y = 1/3 X + c

Since the horizontal intercept is 6,

Y = 0 when X = 6
0 = 1/3 (6) + c
0 = 2 + c
-2 = c

So, we have

Y = 1/3 X - 2

Since Y = x^2 and X = xy,

x^2 = 1/3 xy - 2
1/3 xy = x^2 + 2
xy = 3x^2 + 6
y = 3x + 6/x

It’s different from what we would have done in the correct order, but the given answer is definitely incorrect.

Thanks for the detailed explanation, Mr Eric.
I fully agreed with you and your working solution :)

Really appreciate your effort to assure me with the right working solution.

Once again thank you so much and take care :)