Does ##54/8## have an equivalent fraction with a denominator or ##9##? If so, what is it?

It does not have an equivalent version (with a denominator of 9) and an integer numerator.

Occasionally you may find a teacher looking for (or accepting) fractions with numerators (or denominators) which are themselves fractions.

In this case, we would have the required ratios: ##color(white)("XXX")54/8=x/9##

##color(white)("XXX")rArr 8x=54xx9=486##

##color(white)("XXX")rArr x=486/8=243/4##

and ##54/8 = (243/4)/9##