Because they are fractions which can't be more than one or they are negative
this formula, doesn't rely on a product, relies on a "sum", or is namely an arithmetic sequence, aₙ₋₁ -3 is another way of saying, the value of the previous term minus 3, so it relies on the ordinal value of a term, so is an recursive formula, well, let's get it when n = 4.

Answer:
1 =30 km
1/3=7,5 km
5=150
Im not sure tho but should be fine
4,000
I know this because 2,000 • 2 = 4,000