For this case we have this point given (5,-3) and we want to create an slope intercept formula given by:
And this equation needs to be parallel to y= 3x-1 so then the slope needs to be equal m =3 and then we can use the point given to find the intercept b like this:
If the total cost was 21.35, and the poster cost 8.95, then all you need to do is subtract to poster cost from the total cost to find the cost of the pencil. 21.35-8.95= $12.40