http://mathhelpforum.com/image/png;b...BJRU5ErkJggg==

I have this equation from one of the past papers, but they don't have the solutions.

I know the equation 1a we can solve it using the characteristics method but how about the second one?

The solution for 1a is u(x,t)= x-t^2

I'm confused about the second one.

Can someone show me/explain please.

Thank you