Real numbers are the normal numbers that we use. They are not imaginary.
When you buy a $2809 TV on credit, it means that the amount that you would have to pay is - 2809.
Given that you have to make a $748 advance payment and the rest is paid over 6 months, the balance that you would have to pay over 6 months is
- 2809 + 748
= - 2061
Therefore, the amount that is left to finish paying for the TV is - $2061