Fowards Time in months and days ?

I had a question that asked for the 6 month foward and they gave the 3 month, 6 month , and 1yr risk free interest rate.

I used the 1 year rate based on 60/365 and was wrong the answer was using the 6 month but based on 90/360. I thought that you had to use 365 days for equity fowards and i was ok using the 1 year rate. Any help would be great , i wan to know when to use what.