Hi there let's say A = n+(n+1)+...+(n+k) = (n+(n+k))(k+1)/2 B = (n+k+1)+...+(n+k+m) = (n+k+1+n+k+m)(m)/2 (these are just basic sum formulas, arithmetic series) The left hand side is just A/B, so the final result is (n+(n+k))/((n+k+1)+(n+k+m)) * (k+1)/m I think
