Question

for his long-distance phone service John pays a $3 monthly fee plus $0.11 per minutes, John Long distance bill was $13.23 for how many minutes was John billed?

Answer 1

We can write the bill amount in function of the minutes of long-distance calls (lets call them x) as the sum of a fixed fee ($3 a month) and a variable fee ($0.11*x).

We can write the bill amount in function of x as:

$B(x)=3+0.11x$

If B(x) is $13.23, we can find x as:

$\begin{gathered} B(x)=3+0.11x=13.23 \\ 3+0.11x=13.23 \\ 0.11x=13.23-3 \\ 0.11x=10.23 \\ x=\frac{10.23}{0.11} \\ x=93 \end{gathered}$

Answer: he was billed for 93 minutes.