I need to take total differential of the following:

$\displaystyle M/P = m(y/r)$
$\displaystyle M = s(k,r)B$

I got something like this:

$\displaystyle d(M/P) = ? $
$\displaystyle dM = s_k dk + s_r dr + dB$

($\displaystyle s_k$ simple means the partial derivative of s with respect to k.)

I then need to find out $\displaystyle dr/dk$ and $\displaystyle dr/dB$ but I can do this by myself.