We have to find how many years it will take for the 1300 people to have a cellphone.
This means we have to find x for f(x) = 1300, that is "the number of people using cellphones at time x is 1300".
Then, we can write:
[tex]\begin{gathered} f(x)=1300 \\ 880(1.03)^x=1300 \\ 1.03^x=\frac{1300}{880} \\ 1.03^x\approx1.477 \\ x\cdot\ln (1.03)=\ln (1.477) \\ x=\frac{\ln (1.477)}{\ln (1.03)} \\ x\approx\frac{0.39}{0.03} \\ x\approx13.2 \end{gathered}[/tex]
Answer: it will take 13.2 years for the 1300 people to have a cellphone.
