Question 4
The positive real numbers $a$, $b$, $c$ satisfy the condition:
$$
21ab + 2bc + 8ca \le 12.
$$
Find the least value of the expression:
$$
P(a, b, c) = \frac{1}{a} + \frac{2}{b} + \frac{3}{c}.
$$
$$
21ab + 2bc + 8ca \le 12.
$$
Find the least value of the expression:
$$
P(a, b, c) = \frac{1}{a} + \frac{2}{b} + \frac{3}{c}.
$$