100 POINTS!! PLEASE HELP

A new ball of Stripey String contains 100m of string. It has 10cm lengths of the colours red, blue and white in a repeating pattern of 10cm red, 10cm blue, 10cm white and so on. A new ball of string starts with 10cm of red.

A number of boxes are wrapped separately, in turn, using Stripey String. A new ball of string is used, and no string is wasted in between wrapping the boxes.

For the 1st box, what length of the string used is red?

For the 3rd box, what length of the string used is red?

What is the least total amount of red string that is used for any box, and which boxes in the first 8 use this least amount?

Some toys (wrapped in boxes) are on special offer at 3 for the price of 2. The store decides to stack the 3 boxes on top of each other and use just one piece of string around the stack of 3, with a single bow on top.