Carolyn and Brian Work in an Accounting Office $2.5$ Hours Working Alone It Would Take Brian

Carolyn and Brian work in an accounting office. If they work together they can complete a corporate tax return in $2.5$ hours. Working alone it would take Brian $35$ minutes longer than Carolyn to complete the return. How long does it take each person working alone to finish the job? If a third person is used to help complete the task, and works with the same efficiency as Brian, what is the total time it would take to complete the return if all three work together?