A unit fraction is a fraction with a numerator of 1. With that in mind, we can reduce each of the three given fractions like this:
[tex] \dfrac{12}{84}\div\dfrac{12}{12} =\dfrac{1}{7} [/tex]
[tex] \dfrac{13}{143} \div\dfrac{13}{13} =\dfrac{1}{11} [/tex]
[tex] \dfrac{23}{138} \div\dfrac{23}{23} =\dfrac{1}{6} [/tex]
