How can I solve 8 5/6 - 2 1/3=

There is another method than what the other user has pointed out (both are valid and are up to personal preference as to which are better)

For this method you need to make sure that both the denominators are the same.

(See attached image)

I hope this makes sense!

As a summary; you must make sure that both denominators of the fractions are the same. Whatever number you multiply by for the denominator, use also for the numerator.