Please help me with this question

International calls require the use of a country code. many country codes a 3-digit numbers. country codes do not begin with a 0 or 1. there are no restrictions on the second and third digits. how many different 3-digit country codes are possible?

Which expression do you get when you eliminate the negative exponents of 4a^2 b^216a^-3 b

The product of sin 30 degrees and sin 60 degrees is same as the product of