At 3.5% simple interest it's 39000*10*3.5/100=13,650. It's simple proportion: after one year the interest is 3.5% of 39000=39000*3.5/100=390*3.5. 3.5 is three and a half, and 3*390=1170 plus half of 390 (195)=1170+195=1365. So after 10 years it's 10 times as much=13650.
At 3.5% compound interest where interest is compounded each year the story is different: after one year it's the same as simple interest=1365, but then this is added to 39000 to make 40365. For the second year the interest is 3.5% of 40365=1412.775, added to the interest from the first year=1412.775+1365=2777.775. So after 10 years accumulated compound interest we end up with 16013.35166 interest which boosts the original 39,000 up to 55,013.35 to the nearest cent or penny. Compare this to 52,650 through simple interest.