Answer: He should start cooking the turkey at 12:55 
Explanation:
Hi, to solve this problem we have to analyze the information given: 
So, we have to follow the cooking instructions for over 4kg: 
- 20 minutes per kg + 90 minutes + 30 minutes (rest) 
Now we have to multiply the weight of the turkey by the minutes per kg. 
(20 x 7 )+90 + 30 = 260 min 
260 minutes * 1hr/60 minutes = 4 hours 20 minutes 
And finally, if he plans to carve the turkey at 17:15 
17:15 -4:20 =12:55 
He should start cooking the turkey at 12:55 .