for 1 (a) and (b) press shift cos/tan and then the number 1|2/-1
for 2 and 3 I have no idea/can't be bothered
For 4, use the A = p(1+r/100)^n and sub in each one into the formula
5 - I think same as four but b/c it's compunded monthly for 18 years, n = 18/12
6. Isn't that the same q...