I got 44.6% for 1 b), are u sure you didnt make a typo?
I think ur mistake here is that P=9900
For 2 b) , you forgot to convert weeks back to years, but you also didnt put the correct value of "n"... it is supposed to be 24+3 months, which is 2.25 years
Same for 3 b) "n" is 3 years + 6 months...