The slope/rate of change is m=2
The equation looks like this:
26=x*3.5+8.50
where x is the number of pen you bought.
We solve it like this:
first, we subtract 8.50 from both sides:
17.50 =3.5*x
now we divide both sides by 3.5:
5=x
so you purchased 5 pens.
Writing the slope-intercept form of a linear equation, we have:

Where m is the slope and b is the y-intercept.
Since parallel lines have the same slope, we can see that the slope of the line y = 2/3x + 1 is equal m = 2/3, so for our equation we also have m = 2/3.
Now, using the point (0, -4), we have:

So our equation is:

y = 2/3x - 4
34 divided by 14 is 2.42......
Then multiply it by 6 to get your Y.
that is what I think though, I may be wrong