This is a great argument against working unpaid overtime. Unpaid overtime work holds M constant while reducing T - recomputing your M and T cause M to reduce at a rate of 2.5% per hour worked past 40. And your Q might reduce as well.
M + T*Q = H
What you're looking for is W, the happiness you get from your work. To modify the equation again:
M + T*Q + W = H