im doing multiplying and dividing fractions

i cannot figure the problems out with variable like x
one im working on now is 3/4 divided by 3/x

basic rule:

(a/b) / (c/d) = (a/b) * (d/c)

ie your particular question is (3/4) / (3/x) = (3/4) * (x/3) = x/4

i am looking in my book at the answers after i do a problem and it says the answer to 1/7 devided by 3/x = x-21/7x
and when i done it the way you stated i got x/21

are you sure you are reading the problem correctly?
post it here exactly, best as copy from the book

1/7 divided by 3/x is x/21.

Your book is bad, throw it away.

no i mis read hehe its - not /

good, i worried that it was a textbook teaching creationist mathematics