(5) An 11-digit mobile phone number, the first seven digits are 1390931, if the remaining 4 digits can only be $1, 3, 5$ and each must appear at least once, there are $\qquad$ such mobile phone numbers.
5. 54 Hint: $\mathrm{A}_{3}^{3} \mathrm{C}_{3}^{1} \times 3=54$.

