Question 41480
a)
Cost for 3 days is 25 cents i.e., 3*.25 = .75
Cost for 4 days is 0.75 + 0.05 = 0.80
Cost for 5 days is 0.75 + 0.05 + 0.05 = 0.85
...

Formula would be c = 0.05(d-3) + 0.75 if the days are >=3
Formula would be c = 0.25d if the days is < 3 (i.e., 1 or 2 days)


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b) Substitute d = 7 in the above formula 

 c = 0.05(d-3) + 0.75
 c = 0.05(7-3) + 0.75
 c = 0.20 + 0.75
 c = 0.95 ( 95 cents)