Order of a differential equation is the order of the highest order derivative term present in the differential equation.
Degree of the differential equation is power of that highest order derivative term.
Now, lets take the given differential equation,
d3ydx3+(d2ydx2)3+dydx=xy
The highest order derivative term present is d3ydx3.
⇒ Order is 3 and degree is 1.