Answer:
A. 4·10⁴
Step-by-step explanation:
The problem statement tells you ...
6×10⁵ miles = 15 × (last year's mileage)
Dividing by 15 gives ...
(60×10⁴ miles)/15 = (last year's mileage) = 4×10⁴ miles
_____
Further explanation
An exponent is an indication of repeated multiplication.
10⁵ = 10·10·10·10·10 = 100,000
We can use the associative property of multiplication to rewrite the number of miles:
6×10⁵ = 6·(10·10·10·10·10) = 600,000 = (6·10)·(10·10·10·10) = 60×10⁴
