Draw a Deterministic Finite Automaton $($DFA$)$ that recognizes valid phone numbers in the format xxx$-$xxx$-$xxxx$,$ where the area code $($xxx$)$ must be either $787$ or $939.$

The phone number format is exactly $12$ characters long: $3$ digits $+$ dash $+3$ digits $+$ dash $+4$ digits.

Only phone numbers with area codes $787$ or $939$ should be accepted.

Example of Accepted Phone Numbers:

$787-123-4567$

$939-987-6543$

Example of Rejected Phone Numbers:

$123-456-7890($Invalid area code$)$

$787-12-3456($Incorrect digit count in the second or third group$)$

$7871234567($Missing dashes$)$

Create the DFA by specifying:

The states.

The alphabet $($valid characters$).$

The transition function.

The start state.

The set of accept states.