How do I do “ Converting Measurements between Systems”? Still don’t understand it.

Answer:
B.
Step-by-step explanation:
This expression is a conversion of 8 miles to meters.
mi in the numerator cancels mi in the denominator.
k in the numerator cancels k in the denominator.
You end up with m.
The numbers 8, 1.61, and 1000 are in the numerator, so multiply them together.
Start with 8, multiply by 1.61 and then multiply by 1000.
Answer: B.