100 points answer hurry
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.

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.

here are the choices: 1,9,10,30, 30, 21, 9, 1
make it into a equation with the choices