Solve this formula for m. simplify your answer. S=H/m(a-b)
this should be easy for you. This is just basic algebra. I assume you mean
S=H/(m(a-b))
multiply by m
Sm = H/(a-b)
m = H/(S(a-b))
S=H/(m(a-b))
multiply by m
Sm = H/(a-b)
m = H/(S(a-b))