The y-axis is the line that is vertical in a graph. Four units to the right of the y-axis means that it will be four units above the x-axis, the horizontal line, which means that your x coordinate is 4, your y coordinate can be whatever you want. Ex. (4,1) (4,8)
Well we want to pull out the important values here to determine our expression which in this case is $2 and $.50. Since the fixed cost is 2 and there is .50 per kilometer. We can say that .50(m)+2 is our expression. Hope this helps! I apologize if you were looking for something else in advance.