Make m the subject of the relation h=Mt/d(m+p)

Answer 1

h=Mt/d(m+p)
m+p = Mt/dh
now finish it off

Answer 2

The way you typed it ....
h=Mt/d(m+p)
dh/(Mt) = m + p
dh/(Mt) - p = m

if you meant:
h=Mt/( d(m+p) ) , then
dh(m+p) = Mt
dhm + dhp = Mt
dhm = Mt - dhp
m = (Mt - dhp)/(dh)