Whats the ratio of a width of 21cm to 16cm and a height of 29.7cm to 22.26 cm applied to a height of 9cm and a width of 5.5cm?
This is basically me decreasing the size of a letterhead and wanting to make sure my business card is decreased in size the same ratio

Not actually homework in college but still have no clue how to answer this so any help would be really appreciated!

The ratios of 16:21 and 22.26:29.7 are 0.762 and 0.749 respectively. So I suggest multiplying your dimensions of 9 cm by 0.762, and multiplying 5.5 cm by 0.749.