Lily wants to paint her garden shed. the length, height and width is 2m, 2.5m and 2.6m. she needs to do 2 coats of paint. one tin of paint covers 4m2. how many tins will she need

Assuming the top of the shed has a roof it is not to be painted, the bottom is not to be painted either. dealing with just the sides you only have to calculate 4 panels instead of 6.
unfolding the shed, like it was a piece of folded paper, you now have to only deal with 4 sides.
2.5+2.5+2.6+2.6= 10.2m
10.2m x 2m =20.4 m^2
20.4 x 2 = 40.4 m^2
40.4 ÷ 4 = 10.1
11 tins