VERY IMPORTANT I don't have much time, please answer the question

We have given that , The cooking time for a leg of lamb is 2/5 hours for each pound

We have to find , how long should we cook a leg of lamb that weighs 12 3/4 pounds .How many hours before we have to cook the food so that it will be ready on time for dinner ?

Answer (a) :-

According to the question,

Therefore,

Hence, To cook a leg of lamb weighs 51/4 pounds requires 5 hours 6 minutes

Answer ( b) :-

We have to start cooking before atleast 5.2 hours so that food is ready on the Time for dinner.

5.2 hours because serving and dressing of food also take some time.