Maxima does not seem to come up with an analytic solution to this equation which includes the error function. The independent variable here is "p" and the dependent variable to be solved for is "x". 

[see an illustration of equation follow link](https://i.stack.imgur.com/6XG57.png) 

```
(%i3)   solveexplicit:true$ ratprint:false$ fpprintprec:6$
(%i4)   eqn: (sqrt(%pi)*(25*2^(3/2)*p-25*sqrt(2))*erf(1/(25*2^(3/2)*x))*x+1)/(25*p) = 0.04;
(%i5)   solve (eqn, x);
(%o5)   []
(%i6)   eqn, [p=2,x=0.00532014],numer;
(%o6)   0.04=0.04

```

Any help or pointing in the right direction is appreciated.