Or you can do the reverse step:

Y = mX + c
y = m (y/x) + c

[We always plot VERTICAL against HORIZONTAL, so if they say things like plot x against y, then x is on the vertical axis and y is on the horizontal axis]

With gradient 2 and vertical intercept -1 (here the vertical axis is y and the horizontal axis is y/x),

y = 2 (y/x) - 1

Now we rearrange our variables to make y alone as per the given equation.

Multiplying both sides by x,

xy = 2y - x
xy - 2y = -x
y (x - 2) = -x
y = -x / (x - 2)

where a = -1 and b = 2.

We should actually do this approach using a method in the spirit of this chapter.

Simul by substitution is perfectly acceptable though.

The method I was talking about, in the spirit of this chapter (though almost every student would just do simul instead).

If y = 3x, then y/x = 3

Substituting this into the equation y = 2 (y/x) - 1,

y = 2 (3) - 1
y = 5

[Graphically, this represents X = 3 (i.e. y/x = 3); we trace this on the graph to find the corresponding Y-coordinate; we will get Y = 5 (i.e. y = 5)]

Since y = 5,
y/x = 3
5/x = 3
x = 5/3

Ok tks