Note that subtracting a negative number from another number is equivalent to adding the magnitude of the negative number to the other number. Thus,
subtracting -1 2/3 from 5 1/2 is equivalent to adding 1 2/3 to 5 1/2.
Here the LCD is 3(2) = 6. Let's add 1 4/6 to 5 3/6. We get 6 7/6, or more properly, 7 1/6 (answer).
