Area codes are the first three digits of a 10-digit telephone number. The first digit of an area code cannot be 0 or 1. a. How many area codes can be created if digits are allowed to be repeated?

b. How many area codes can be created if digits are not allowed to be repeated?

PLEASE HELP this is a timed quiz

To keep cylindrical tanks from tipping over, a designer is planning to enlarge the original area of the base by 50%. the new tank should have the same volume as the original. how should the designer change the height of the tank? a: make it 50% taller than the height of the original tank. b: make it 6623% taller than the height of the original tank c: make it 3313% shorter than the height of the original tank d: make it 50% shorter than the height of the original tank.