The Coordinate Plane · Hard problem

Nora and Ben each save money every week. Nora plots her savings as points (week, dollars): $(0, 12)$, $(1, 17)$, $(2, 22)$, and so on. Ben's points are $(0, 40)$, $(1, 43)$, $(2, 46)$, and so on. Both keep saving at the same rate. In which week will their points have the same $y$-coordinate?