Given, differential equation is
\((\frac{d^2y}{dx^2})^2 + (\frac{dy}{dx})^3 + x^4 = 0\)
Here, we see that the highest order derivative is \(\frac{d^2y}{dx^2}\), whose degree is 2.
Here, order = 2 and degree = 2
Thus, sum of the order and degree = 2 + 2 = 4