Jonathan purchased 30 bags of mulch to spread in his garden. The graph shows points representing the number of bags of mulch left to spread at several different times while Jonathan is working.

A function graph of a line segment having three points (0,30), (1,21) and (2, 12) with an x axis of zero to four Hours and a y axis of zero to thirty five Bags of mulch left



Select from the drop-down menus to complete the equation, in standard form, that represents the relationship between the number of bags of mulch left to spread, y, and the time, x, Jonathan has spent mulching.