Skyscraper: Focus on column 9. There is a 7 clue at the bottom. So R9C9 can take values 1,2 or 3. If it takes any other value you cannot see seven buildings from that direction. Similarly R2C9 and R5C9 can also have 1,2 or 3. So we get a triplet in Column 9. The other cells must have the numbers from 4 to 9 and there is only one way you can place them to satisfy the 7 clue for the column.

Octopus link: The four 6x6 sudokus contain the linked example . Solve the inequality. You can solve it independently. Now look at column 1 for a common digit across all 4 sudokus. You should be able to eliminate everything except the 5 in r5c1.