First, let's convert 6 feet 3 inches to just inches. Because there are 12 inches in 1 foot, we can say that there are 72 inches in 6 feet. Combined with the other 3 inches, we can say that Marco is a 75 inches tall.
Now, we can multiply the number of inches we found by 2.54 to get Marco's height in centimeters. This gives us 190.5 cm.
There would be 25 girls. You would turn it into a fraction and times both by 5 to get 20/25. 5/4=1.25 and 25/20=1.25 in case you need to check your work