Answer
a) $20^{2} = 400$
b) $20^{3} = 8000$
c) $20^{4} = 160000$
Work Step by Step
For each of the 2/3/4 components of a molecule made up of amino acids, we can choose from 20 options as there are 20 different types of amino acids out there. The options for a molecule composed of 2 amino acids are found by combining each unique amino acid with itself and the other 19 amino acids resulting in 400 options. For 3 components we've got 20 x 20 x 20 options and for 4 components 20 x 20 x 20 x 20.
