A photocopy store advertises the following prices: 5/c per copy for the first 20 copies, 4/c per
copy for the 21st through 100th copy, and 3/c per copy after the 100th copy. Letx be the
number of copies, and let y be the total cost of photocopying. (a) Graph the cost as x goes
from 0 to 200 copies. (b) Find the equation in the form y = mx + b that tells you the cost
of making x copies when x is more than 100
It's impossible to tell what you did wrong if you don't show what you did or even what result you got!
How much will it cost to make 100 copies? that is 20 at 5 c each, 80 at 4 c each.
How many will it cost to make 200 copies? Again, that is 20 at 5c each and 80 at 4 c each, plus 100 at 3 c each. Once you know the cost for 100 and 200,
put those as "y" values in y1= m(100)+ b and y2= m(200)+ b and solve for m and b.
(Yes, the y-intercept of this function is $1.20.)
..and as Halls asked what was your answer and argument to support it?
By the way the book answer is wrong unless there is more in the question than you posted. The question is formulated in cents but the book answer given in dollars, now if it says it wants the answer in dollars that is different.