Awan co december 2013

My first question is related to FRAS
Sir i solved the way as
If int rate increases by 0.9%
Actual return on deposit
( 48m×4.79%×4/12) $766400
Payment to voblaka bank
(4.82%_4.79%×48m ×4÷12) 4800
Net return 771200

But when i am looking answer at the back while calculating payment to voblaka bank they used( 4.99%_4.82%×48m×4/12)… i think they should have used 4.79% instead of 4.99%) please explain and correct me

2 i have doubt in part b theory which says how delta value of an option could be used in determining the No of contracts purchased i cannot understand this part please guide