Convert your feet-and-inches into ONLY inches, then subtract Sister's height from Danny's.
Given = there are twelve inches in one foot
6 feet 1 inch = ? inches
6 feet = 6 x 12" = 72 inches + 1 inch
Danny is 73 inches tall.
5 feet 6.5 inches = ? inches
5 feet = 5 x 12" = 60 inches + 6.5 in
Sister is 66.5 inches tall.
Now, subtract Sister's height from Danny's height:. 73in - 66.5in = 6.5in
Danny is 6.5 inches taller than his sister.