What are the steps for adding and subtracting mixed numbers with unlike denominators

Well, there are different ways to do this if you are really familiar with fractions, but "officially" :P

1) convert mixed numbers to improper fractions.

rule:  a b/c = (ac+b)/c

2)  make all fractions have a common denominator...

a/b+c/d

(a/b)(d/d)+(c/d)(b/b)

(ad/bd)+(cb/bd)

3)

The simplify your final answer with greatest common denominator or convert back to mixed number if needed...

That’d be 9 years or something