In how many ways can 4 prizes be given to 3 boys when a boy is eligible

Let suppose 4 prizes be $P_{1}, P_{2}, P_{3}, P_{4}$ and 3 boys be $B_{1}, B_{2}, B_{3}$

Now $P_{1}$ can be distributed to 3 boys $\left(B_{1}, B_{2}, B_{3}\right)$ by 3 ways,

Similarly, $P_{2}$ can be distributed to 3 boys $\left(B_{1}, B_{2}, B_{3}\right)$ by 3 ways,

Similarly, $P_{3}$ can be distributed to 3 boys $\left(B_{1}, B_{2}, B_{3}\right)$ by 3 ways,

And $P_{4}$ can be distributed to 3 boys $\left(B_{1}, B_{2}, B_{3}\right)$ by 3 ways

So total number of ways is $3 \times 3 \times 3 \times 3=81$