Multi part function problem

Darden Restaurants, Inc. owns a number of popular restaurants. According to the company's 2005 report the cost of sales increased from $3.1 billion in 2001 to $4.1 billion in 2005. During the same time period, revenue from sales increased from $4 billion to $5.3 billion.

a) Between 2001 and 2005 was the cost of sales increasing more rapidly than the revenue?

b) What is an equation of a linear function that models revenue from sales as a function of cost from sales?

c) Given the model you found in b) what do you estimate the revenue was when the cost of sales was $3.9 billion?

d) According to the company's report the cose of sales was $3.9 billion in 2004 and the revenue from sales was $5 billion. How well did your esimate in part c) fit the actual data?

This is only my second post, so again I'll say, if I did anything wrong with how or where I posted this please just let me know!

Thanks so much for ANY help on this problem!

Re: Multi part function problem

Hey NRK0208.

Usually we ask people to post their attempts at a question so we can best help them.

Hint: A linear function (relationship between variables) for two variables is y = mx + b for some constants m and b.

Re: Multi part function problem

Okay I'll be sure to do that in the future! Thanks for letting me know..

For a) I said that the revenue was increasing faster simply because the difference was greater than the difference of the sales.

Then for b) my class partner got the equation y=x(1+2.6)^.2 but she could not explain to me how she got this. (She is an exchange student so there's some communication problems..) When I plug 3.9 into this equation as x for part c) it gives me 5.04 billion, which is about what the answer should be (per part d.)

So some explanation as to that equation would be so helpful thanks in advance!!