Like 17 probably.
12 straws
I need 100 straws.
8 straws.
6
18 straws.
The number of hexagons that can be made with 48 straws depends on the length of the straws and how many straws are used per hexagon. A standard hexagon has 6 sides, so you would need 6 straws to make one hexagon. Therefore, with 48 straws, you can create 48 / 6 = 8 hexagons.
6
6 of them
15 straws are needed
12
Put many straws together to make it stronger
That's going to depend on what shape you're building, which, as far as I can see, you neglected to mention.