The differential equation for all family of line which are at a unit distance from the origin is

The differential equation corresponding to the family of curves $y=e^x(a x+b)$ is

If $$m$$ and $$n$$ are order and degree of the question $$\left(\frac{d^2 y}{d x^2}\right)^4+8 \frac{\left(d^2 y / d x^2\right)^3}{\left(d^4 y / d x^4\right)^5}+\left(\frac{d^4 y}{d x^4}\right)=x^2+4$$, then $$m-n$$ is equal to

The solution of $$d y / d x=1+x+y+x y$$ is