long-distance calls from New York to Harare are priced at 85 cents/min off peak and $1.20/min at peak times.

Question

a_ draw, on the same exes, conversion graphs for the two different rates.
b_ from your graph estimate the cost of an 8 minute call made off peak.
c_ estimate the cost of the same call made at peak rate.
d_a call is to be made from a telephone box. if the caller has only $4 to spend, estimate how much more time he can talk for if he rings at off speak instead of at peak times

Answer 1

At off peak rate:
cost = .85t

at peak time rate:
cost = 1.2t

I can't do the graphs for you, but I suggest for the first you use:
(0,0) and (20, 17) to sketch the first graph, and
(0,0) and (20, 24) for the second one

sub t = 8 into off-peak equation
and into the peak equation to check your estimated costs

for the last part go up to 4 on the vertical axis and run horizontal till you meet the lines.
or
to get the actual answers .....
4 = .85t
t = 4/.85 = appr 4.7 minutes

4 = 1.2t
t = 4/1.2 = 3 1/3 minutes