You just have to add each amount of snow to figure out the total. This will get you 10.989
3 buckets covers 90m x 80cm = 3 buckets for 90x0.8 = 3 for 72
x buckets covers 200m x 120cm = x buckets for 200x1.2 = x for 240
3/72 = x/240
720 = 72x
x =10 buckets of paint to cover 200mx120cm fence
