Can any1 solve this? it's a brain teaser...?

91. If you look at each column, you can see a pattern. columns 1 2 and 3 (from the left) all increase by 1 down the column. Column 5 increases by 8, 10, 12, etc., meaning the amount of increase increases by two per number. Column 4 increases by 13, 17, 21, etc., meaning the amount of increase increases by 4 per number. so that makes the number you are looking for 91. 15+13=28; 28+17= 45; 45+ 21=66; 66+25=91