Solving piecewise defined functions for x

Hello,

I want to solve a piecewise defined Function:

PiecewiseFunction(x):= |x if x >= 0

|3x otherwise

PiecewiseFunction(x)=3 solve --> (in the german version the word "solve" is replaced by "auflösen", so I'm not sure if solve is the right syntax there)

But this doesn't work on piecewise functions. The error message is that the value must be a scalar.

Does anyone know how to proceed in this case?

Regards