Algebra 2
posted by Jessica .
A photocopying machine purchased new for $4500 loses $900 in value a each year.
a. Find the book value of the machine after 18 months.
b. When will the book value be $1200?
Assume that each situation can be decribed as a linear equation
HELP!!! I don't know how to set this up but I know the answer

Value = 4500  900t, where t is the number of years
a) 18 months > t = 1.5
value = 4500  1.5(900) = 3150
b)
solve
1200 = 4500  900t 
the charge for a one day rental of a car from Hawks car rental agency is $24 plus 15 cents for each mile driven.
a) If sarah drives 85 miles in one day, how much is the charge?
b) If a one day rental cost Sarah $42, how far did she drive?