2011 mock exam Q39 examples, interest, decrease, effective, 2011

DoubleDip

The question asks to compute the effective interest rate when loaning out LIBOR+spread and using put option to protect against decrease of interest rate.

I got the 6 month return rate right, but I annualized the rate by (1+r)^2-1. The provided answer and textbook examples used (1+r)^(365/180)-1.

Can someone explain the day count convention here? The question specifically states the day count convention for the option is 30/360.

Thanks!