The following image was made from Subtract Fractions Designer:

Subtraction with Fractions - Strict is similar to the previous program SUBTRACT FRACTIONS except that the difference must be entered as a mixed or whole number and in lowest terms.

The picture shows that the minuend is 3 5/6 units in length and the subtrahend is 2 1/3 units in length. The difference can be found by determining the distance from the end of the subtrahend to the end of the minuend. For example the distance from 2 1/3 to 3 is 2/3 units and the distance from 3 to 3 5/6 is 5/6 units. Just add 2/3 and 5/6 for the difference of 1 3/6 or 1 1/2 units.

You may prefer to work vertically:

See the program MIXED NUMBERS for information on writing fractions in mixed form.

See the program RENAME
IN LOWEST TERMS for information on writing fractions in lowest
terms.