A mixture contains two chemicals, A and B, with masses mA and mB. The total mass of the mixture, m, remains constant. B is converted into A at a rate that

is inversely proportional to the mass of A and directly proportional to the square of the mass of B in the mixture at any time t.

Form a differential equation and
find a general expression relating the mass of A to the time t.

ive got dma/dt = mb^2/ma

is this right and how do i do the next bit

dmA/dt = cmB^2/mA

where c is a constant
mB=m-mA so
dmA/dt = c (m-mA)^2/mA
= (c/mA)(mA^2-2mmA+m^2)
= cmA-2cm+cm^2/mA
integrate with respect to t