22. A worker takes a time ratio of $1: 2: 3$ to make 1 $\mathrm{A}$ part, 1 $\mathrm{B}$ part, and 1 $\mathrm{C}$ part, respectively. He can make 2 $\mathrm{A}$ parts, 3 $\mathrm{B}$ parts, and 4 $\mathrm{C}$ parts in 10 working hours. If he needs to make 14 $\mathrm{A}$ parts, 10 $\mathrm{B}$ parts, and 2 $\mathrm{C}$ parts, the required working hours are ( ).
(A) 12
(B) 15
(C) 18
(D) 20
Answer: D.
Solution: Let the worker need $x$ hours to make 1 part $\mathrm{A}$, then the hours he needs to make 1 part $\mathrm{B}$ and 1 part $\mathrm{C}$ are $2 x$ and $3 x$ respectively. According to the problem, we have
$$
2 x+3 \times 2 x+4 \times 3 x=10,
$$

Solving for $x$, we get
$$
x=0.5 \text {. }
$$

Therefore, to make 14 parts $\mathrm{A}$, 10 parts $\mathrm{B}$, and 2 parts $\mathrm{C}$, he needs
$$
14 x+10 \times 2 x+2 \times 3 x=40 x=40 \times 0.5=20 \text { hours. }
$$

Hence, the answer is D.