Within an area code, phone numbers consist of 7 numbers, if non of the first three numbers can be zero or one, how many different phone numbers are possible within an area code

The 8*8*8*10*10*10*10 or 5120000 possible numbers.

Why?

When dealing with possible number combinations, we have to look at how many
numbers we are allowed to use for each input.

For the first three digits, we can use the numbers 2 to 9, a total of 8 numbers each. For the last 4 digits, we can use the numbers 0 to 9, a total of 10 numbers each.

We then multiply the amount of numbers each digit can hold, so 8*8*8 for the first three, and 10*10*10*10 for the final four. Combined, it would be 8*8*8*10*10*10*10, which would simplify to 5120000.