What is the interpretation of the coefficient attached to the Cost ($) variable?

Profit ($) = 100 - 0.9 Cost ($)

Select one:

a. If the Cost increase by 0.9 $, the profit will increase by 1 $

b. If the Cost increase by 1 $, the profit will decrease by 0.9 $

c. If the Cost increase by 1 $, the profit will decrease by 1 $

d. If the Cost increase by 1 $, the profit will increase by 0.9 $