Description for Correct answer:
Given that \( \Large n \left(A\right)=3 \) and \( \Large n \left(B\right)=4 \), the number of injections or one-one mapping is given by.

\( \Large ^{4}p_{3} \frac{4 !}{ \left(4-3\right)!}= 4 \times 3 \times 2 \times 1 = 24 \)