I think it is 15, just by looking at it
2) The area is 1.1 m^2 because to find the area the formula is width*length. SO you would separate it. It would be 0.9 * 1 = 0.9 and 0.4 * 0.5 = 0.2. Then you add it together. So it would be 1.1 m^2. The perimeter is all the sides added together so 4.2 m, but it says mm so you have to convert it and you get 4200.
4) Area is 1.16 cm^2. Again you would seperate it. So, 1 * 1 = 1 and .2 * .8 = .16. Then you add it together and get 1.16 cm^2. The perimeter is all the sides added up. You get 4.2 cm.
It depends on what type of Triangle or what the volume or area is. This question is missing information.
