Simple interest would come to 6×3=18% in 6 months.
18% of $3298=3298×0.18=$593.64 interest.
If it's compound interest (compounded monthly) then the solution is different.
End of 1st month, interest would be $98.94 (3% of $3298) so the amount would become $3396.94.
End of 2nd month, interest would be $101.9082 (3% of $3396.94) so the amount would become $3498.8482.
End of 3rd month the amount becomes $3603.81(3646).
End of 4th month the amount becomes $3711.92(8055).
End of 5th month the amount becomes $3823.28(5897).
End of 6th month the amount becomes $3937.98(4474). The interest is $3937.98-$3298.00=$639.98.
Compare this with $593.64 and you can see that compound interest works better by $46.34.