Answer: d. 44 times higher
Step-by-step explanation:
The benefits of cleaner air was $22 trillion and the cost of reducing pollution was $500 billion.
The number of times that you would have to multiply this cost of reducing pollution to get to the benefits of cleaner air is:
= 22 trillion / 500 billion
= 22,000 billion / 500 billion
= 44 times higher