Can we have a repeating number in a fraction? For example, repeating 54 over positive 6.

No we cant. Fractions when simplified can be a repeating number like 1/3 but you cant have like 54.545454/2. You can turn a repeating decimal into a fraction but it doesn't work the other way. Its just how math works. Same thing as how you can; t have a decimal in a fraction. You always need to simplify the fraction if it has a repeating number or a decimal. Its just how it works. Sorry if I can't explain it too well

Yes. All you have to do is simplify the fraction to its lowest term.