Which of the following transformations reduce the differential equation $\frac{d z}{d x}+\frac{z}{x} \log z=\frac{z}{x^2}(\log z)^2$ into the form $\frac{d u}{d x}+P(x) u=Q(x)$

Solution of the differential equation $y \frac{d y}{d x}+x=0$ represents a family of

The solution of $(x+\log y) d y+y d x=0$ when $y(0)=1$ is

The order of the differential equation $\frac{d}{d x}\left[\left(\frac{d y}{d x}\right)^3\right]=0$ is