For the first 5 years of a cow's life, the weight w (in kilograms) of the cow approximately fits the formula w(t)=40+90t, where t is the age of the cow in years.

which of the following is the most accurate interpretation of the slope of the line represented by this formula?

a. the slope is 40. this means that the cow gains on average 40 kilograms per year for the first 5 years of its life.

b. the slope is 90. this means that the cow gains a total of 90 kilograms in the first 5 years of its life.

c. the slope is 40. this means that the cow gains a total of 40 kilograms in the first 5 years of its life.

d. the slope is 90. this means that the cow gains on average 90 kilograms per year for the first 5 years of its life.