If $m$ and $n$ are respectively the order and degree of the differential equation $\left(\frac{d^2y}{dx^2}\right)^2+\left(\frac{dy}{dx}\right)^3+y=4x$, then the value of $m + n$ is:

4

The correct answer is Option (3) → 4

$\text{DE: }\left(\frac{d^{2}y}{dx^{2}}\right)^{2}+\left(\frac{dy}{dx}\right)^{3}+y=4x$

$\text{Order }(m)=2$

$\text{Degree }(n)=2$

$m+n=4$