You have to turn them in to the lowest common denominator
This should be right! $5,000 + $1,000x
Let a ∈ A. Then a is some integer that is divisible by 4, so we can write a = 4k for some integer k.
We can simultaneously rewrite a as a = 2•2k, so 2 clearly divides a, which means a ∈ B as well.
Therefore A ⊆ B.
The conference call lasts 90 minutes. Minutes at daytime rate is 7pm to 8pm, 60 minutes, and at nighttime rate, 30 minutes.
60 mins @ 5c/min=$3. 30 mins @ 3c/min=$0.90. Total before conference charge: $3.90. Total cost=3.90×1.5=$5.85.
