Transcript text: Determine the order of the given differential equation and state whether the equation is linear or nonlinear.
\[
\frac{d^{4} u}{d r^{4}}+\frac{d u}{d r}+5 u=\cos (r+u)
\]
(a) The order of this differential equation is $\square$
(b) The equation is $\square$ Choose