It is written partially in <em>Slope-Intercept Form</em> [y = mx + b]. That 4 is your <em>y-intercept</em><em>,</em><em> </em>which means it is shifted upward; it is written as [0, 4], but at least you get the idea.
Painting USA is better for part 1 because they will charge him $700 and if it takes 5 hours to paint the house they will charge the same amount. Hope this helps.