With any fraction, no matter what its denominator (bottom part), you multiply the numerators (tops) by each other and the denominators (bottoms) by each other.
For example,
[tex] \dfrac{5}{4} * \dfrac{8}{7} = \dfrac{(5)(8)}{(4)(7)} = \dfrac{40}{28} = \dfrac{10}{7}[/tex]
