Final answer:
Wang Yong paid $170 each month and it took him 38 months to pay back his entire debt.
Step-by-step explanation:
To find out how much Wang Yong paid each month, we can subtract the remaining debt from the initial debt and divide it by the number of months. In this case, $(8500 - 6460) = $2040 is the amount he paid over 12 months. So, Wang Yong paid $(2040 / 12) = $170 each month.
To calculate how long it took Wang Yong to pay back his entire debt, we need to divide the remaining debt by the monthly payment amount. $(6460 / $170) = 38. So, it took Wang Yong 38 months to pay back his entire debt.