1000×12× 7.5/1000 = the second payment in 90 yuan.

Actual profit =12000-10000-75-90 =1835 yuan.

2) Let the annual profit be x%

1000+ 1000 x %×3 = 1086.7

Solution: x=2.89%

3) Let the annual profit be x%

5000+5000x%×2=5500

Solution: x=5%