A food truck vendor averages 150 tacos sold when the price per taco is $4 . A study shows that the average number of tacos sold will increase by 25 tacos for every $1 that the price per taco is lowered.

Which equation models the food truck's average sales in dollars, s, in terms of the price per taco, x?

s = 25x + 250
s = -25x + 250
s = 25x^2 + 250
s = -25x^2 + 250