The monthly cost of producing x electronic components is c(x)=2.15x+2350 c. what is the domain of the average cost function?

The domain is the interval within which the values of x are meaningful/possible.

In the case of cost function, since we do not produce negative quantities of components, and there is no upper limit imposed on the production amount, the domain of the average cost function is therefore from zero to infinity (but excluding latter).
Written in interval notation, the domain is
Dom(C(x))=[0,infinity)