Here is the question : comute and simplify 19/7 & 8/21?

I know you have to flip 8/21 to make it 21/8 then you times the denominator and numerators then divide the numerator into the denominator but thats where im messing up at i know it would be 56 divided into 399 which makes it on the calculator 7.125 but of course the calculator doesnt write in fractions so im stuck on how to get the answer i need detailed steps please....Sorry im math illiterate i guess and obviously half-way retarded....but thanks to all in advance for help...cause i need it.