Let's compare apples to apples and oranges to oranges: convert each given proper fraction into its decimal counterpart:
3 63/80 => 3 .788 approx.
3 1/5 => 3.2
3 11/20 => 3.55
It's now an easy matter to arrange these numbers from least to greatest:
3.2, 3.55, 3.79, or
3 1/5, 3 11/20, 3 63/80