What formula should I use to solve this problem? (Could you show steps with formula)

A and B own equal shares in an apartment as tenants in common. B lives in another state, but A lives in the apartment, whose rental value if $1,000 per month. B refuses to contribute to paying the mortgage, property taxes, and insurance on the apartment. A sues B for an accounting and contribution to these carrying costs. What result if the carrying costs are $500 per month? What result if these costs are $1200/month?