Step-by-step explanation:
so, we have 4 positions with letters.
that means we have 26 possibilities per position.
that makes 26⁴ possibilities there.
and then we have 3 positions with digits.
the means 10 possibilities per position, and so 10³ = 1000 possibilities there.
the total number of possible different account numbers is then
26⁴ × 1000 = 456,976,000
