I need to take total differential of the following:

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

I got something like this:

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

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

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