Question 1089848
We have a formula for the total cost of a call:
{{{f(x) = 0.75x + 1.50}}}
Remembering that x is the number of the minutes of the call, we know that a 7.5 minutes call implies that x = 7.5.  So,
{{{f(7.5) = 0.75*7.5 + 1.50 = 5.625 + 1.50 = 7.125}}}
However, money does not contain a third decimal place, so we need to round to pennies, meaning that the cost of a 7.5 minute call would be $7.13.