Make all of them either a decimal or all as fractions. the least is the furthest from 0 if it on the left side of 0 on a number line. Negatives are to the left.
-3 and 1/8 = -3.125
-3 and 1/4 = -3.25
so your numbers are now
-3.25, -3.125, -3.25, -3.1
Least to greatest
-3.25, -3 1/4, -3 1/8, -3.1
