An easier way to do this is to make the fractions improper fractions.
3 1/6 can be rewritten as 19/6. 1 4/6 can be rewritten as 10/6. (Multiply the denominator by the number at its side, and add it to the numerator).
2 3/6 is 15/6.
Subtract 10/6 from 19/6.
19/6-10/6=9/6.
9/6 is not 15/6, therefore she did not use 2 3/6 yards of fabric.
