Your question is missing some elements but to answer the question I have to make an assumption.
Assuming that she make a monthly payment of $75.
The value of an loan at the end of the two year is given by
[tex]FV=PV(1+r)^n[/tex]
where PV = $799, r = 7.2% = 0.072 and n = 2 years.
Thus,
[tex]FV=799(1+0.072)^2=799(1.072)^2=799(1.149184)=\$918.20[/tex]
If she makes a monthly payment of $75, the number of months it will take her to pay off for her laptop is given by
[tex] \frac{\$918.20}{\$75} =12.24\, months[/tex]
Therefore, it will take her 13 months to pay off for the laptop.
