A landscaper buys a new commercial grade lawn mower that cost $\$3000$. Based on past experience he excepts it to last about $7$ years, and then he can sell it for scrap metal with salvage value amount $\$250$. Assuming the value of the lawn mower depreciates at a constant rate, which depreciates at a constant rate, which equation could be used to find its approximate value after $x$ years, given that $x <7$

Question

$(a)\;y=-7x+2500 \\ (b)\;y=-250x+3000 \\ (c)\;y=250x+3000 \\ (d)\;y=-250x-3000$