Given:
The cost to call China as a function of the time, in minutes, t, on the phone is
[tex]c(t)=1.75+0.85(t-1)[/tex]
To find:
The time when the cost first exceed $57.
Solution:
The cost first exceed $57 means cost is greater than $57.
[tex]c(t)>57[/tex]
[tex]1.75+0.85(t-1)>57[/tex]
[tex]0.85(t-1)>57-1.75[/tex]
[tex]0.85(t-1)>55.25[/tex]
Divide both sides by 0.85.
[tex]t-1>\dfrac{55.25}{0.85}[/tex]
[tex]t-1>65[/tex]
[tex]t>65+1[/tex]
[tex]t>66[/tex]
Therefore, after 66 minutes the cost to call china will exceed $57. It means first at t=67 the cost will exceed $57.
