A unit fraction is any fraction with a one in the numerator. 1/6, 1/12, 1/432 are all unit fractions. This question is simply asking you to add the number of unit fractions in 4/6. There are 4 unit fractions in 4/6.
1/6 + 1/6 + 1/6 + 1/6= 4/6
Hope this helps! :)
