Agardener is planning to fill her garden with mulch. she plots it on a grid to plan how much she will need. the garden is in the shape of a rectangle with vertices at (2, 5) (8, 5) (8, 3) and (2, 3). one bag of mulch covers 6ft2 and costs $5.25. how much will it cost her to cover her garden?

First is to know length and width of the rectangular garden. 
length of the garden is difference in the x coordinates
L = 8 - 2 = 6 ft
while the width is the difference in the y coordinates

w = 5 - 3 = 2 ft

now we can solve the area of the rectangular garden.
A = Lw
A = 6 x 2 = 12 sq ft

Cost = ($ 5.25 / 6 sq ft) x ( 12 sq ft)
cost = $ 10.5