Question: Problems with plot

Here's what i have to do. i have a system formed of 3 equations, and i have to find the solutions ( there may be only one ), and the make sinus out of it evaluating it with 5 digits.

I am finding problems with plot first:

f:=x+y+z=1; g:=3*x+2*y-z=5; h:=x*y+7*z^3=0;

plot:-implicitplot([f,g,h],x=-2..2,y=-2..2,z=-2..2);

I get this error: Error, (in plots/implicitplot) invalid input: the following extra unknowns were found in the input expression: {z}

I wanted to use plot to see how many solutions i have.

I also used fsolve, but i know fsolve only gives you one solution:

> fsolve({eqn1, eqn2, eqn3});
            {x = 11.27679579, y = -13.03572772, z = 2.758931931}
 

and now i want to obtain the value for sin(x+y+z) with evalf[5].

how can i tell MAPLE how to get the x,y,z values that fsolve found for me ?

Thanks in advance!