Solve the Problem. -Mark Can Remember Only the First 4 Digits of His

Multiple Choice

Solve the problem.
-Mark can remember only the first 4 digits of his friend's phone number. He also knows that the number has 7 digits and that the last digit is not a 0. If Mark were to dial all of the possible numbers
And if it takes him 21 seconds to try each one, how long would it take to try every possibility?

A) 35 minutes
B) 10.5 minutes
C) 350.1 minutes
D) 315 minutes