if x=1+ mn/m+n,make m the subject of the relation
I have a mathematical feeling that you meant:
x= (1+ mn)/(m+n)
then
xm + xn = 1 + mn
xm - mn = 1 - xn
m(x - n) = 1 - xn
m = (1 - xn)/(x - n)
let me know if I was wrong in my interpretation and you meant
it the way you typed it. Brackets are soooooo important here!