Integer Linear Programming

Hi guys..this is an operations research question. I have been having problems formulating the objective function. Hopefully, I can get some help on it. I am required to formulate and solve an integer programming problem. The question is as follows:

There are 5 helicopters available to transport a list of items from 1 place to another. Each helicopter can carry up to 200kg. Each helicopter has 4 seats. All items must be transported. The weights of items are listed in the list below:

Item No Weight
1 20
2 16
3 6
4 6
5 101
6 10
7 8
8 95
9 111
10 120

The constraints are Item No.1 must be carried in the first helicopter.
Items No. 9 and 10 are not allowed to be on the same helicopter.
Items No.6 and 7 need to be on the same helicopter.

I would think that the objective function is to minimize the number of helicopters used since a cost is associated with the hiring of each helicopter. Hence, the objective function will be something like minimise no of helicopters used. Just stuck on formulating the part after that.