First, let's calculate the amount earned after he sold the car:
[tex]90\text{\% of 56000}=0.9\cdot56000=50400[/tex]Then, let's subtract 1310 from this value:
[tex]50400-1310=49090[/tex]Finally, we can calculate the interest earned using the formula for simple interest:
(I is the interest, P is the principal, i is the interest rate and t is the time)
[tex]\begin{gathered} I=P\cdot i\cdot t_{} \\ I=49090\cdot0.06\cdot3 \\ I=8836.2 \end{gathered}[/tex]Therefore the interest is $8836.20.