B) A typical telephone number in the United States is of the form NXX NXX XXXX, where the Ns are digits other than 0 or 1 and the Xs are any digits. The first 3 digits constitute the area code. Find...

need correct and urgent

Extracted text: B) A typical telephone number in the United States is of the form NXX NXX XXXX, where the Ns are digits other than 0 or 1 and the Xs are any digits. The first 3 digits constitute the area code. Find the minimum number of area codes needed to serve a 23-million-subscriber area.