Multiplying fractions, unlike adding them, does not require you to find a common denominator. Simply multiply the numerator and denominator and simplify if you have to. In this case, it's [tex]\frac{-3}{5} * \frac{1}{8}[/tex].
--> [tex]\frac{-3 * 1}{5 * 8}[/tex]
A negative multiplied by a positive is still negative, so this becomes [tex]-\frac{3}{40}[/tex].