This is the ground plan of a group of square sky|scrapers. In every row and column there is one buil|ding with 10, 20, 30 and 40 (and in larger puzzles also 50 and 60) floors but you do not know in which order. The num|bers at each side indi|cate how many buil|dings can be seen in the repec|tive row or column from this side. Higher buil|dings hide lower buildings. Write the height of each building into the squares on the ground plan.