Use the rule of proportion to solve for H and A in the given problems.

$$
15 \times H = 30 \times 12
$$

$$
H = \frac{30 \times 12}{15}
$$
$$
H = 2 \times 12
$$
$$
H = \boxed{24}
$$

$$
18 \times H = 29 \times 16
$$

$$
H = \frac{29 \times 16}{18}
$$
$$
H = \frac{29 \times 8}{9}
$$
$$
H = \frac{232}{9}
$$
$$
H = \boxed{25.78 \text{ (लगभग)}}
$$

$$
14 \times H = 10 \times 35
$$

$$
H = \frac{10 \times 35}{14}
$$
$$
H = \frac{5 \times 35}{7}
$$
$$
H = 5 \times 5
$$
$$
H = \boxed{25}
$$

$$
H \times 3 = 15 \times 16
$$

$$
H = \frac{15 \times 16}{3}
$$
$$
H = 5 \times 16
$$
$$
H = \boxed{80}
$$

$$
30 \times 20 = 5 \times A
$$

$$
A = \frac{30 \times 20}{5}
$$
$$
A = 6 \times 20
$$
$$
A = \boxed{120}
$$

$$
50 \times 18 = H \times 30
$$

$$
H = \frac{50 \times 18}{30}
$$
$$
H = \frac{5 \times 18}{3}
$$
$$
H = 5 \times 6
$$
$$
H = \boxed{30}
$$