In 2002 the cost of a textbook was $120.00 and in 2013 it was $212.00. 

a. Assuming the cost of the textbook increases linearly as a function of time, give the function of the cost of the textbook since 2002. 

 

b. Give the interpretation of the slope of the function in part (a). 

 

c. A book is considered to be unaffordable when its price is more than $300.00. If the increase in price follows this linear trend, when will the book be unaffordable? 

Here are some hints:

What have you tried so far?
Do you have an idea how to start?
Does it help to draw a simple picture using time as x-axis and price as y-axis?

Thank you

Any linear function of x can be written f(x)= ax+ b for numbers a and b.  You are told that f(2002)= 120= 2002a+ b and f(2013)= 212=  2013a+ b.  Solve  the equations 

2002a+ b= 120 and 2013a+ b= 212 for a and b.