It is shown that the profitability i is given by (8) and (9).
From (1) we have
From (7) and (B1) follows that
Comparing the right-hand side of (B2) and the left-hand side of (A2) it is easy to see, after replacing x by g in (A2), that analogously with (A9) it follows from (B2) that
After some algebra (B3) can be written as
Denoting
(B4) becomes
Solving i from (B5) gives (8).