Answer:
20
Explanation:
lets label each shirt as A, B, C, D, E and each pair of pants as a, b, c, d
combinations include:
Aa, Ab, Ac, Ad, Ba, Bb, Bc, Bd, Ca, Cb, Cc, Cd, Da, Db, Dc, Dd, Ea, Eb, Ec, Ed
however, it isn't necessary to write out all the combinations as you could just do 5*4=20.