Answer: B) 8•10^-1
Use the commutative property to reorder the terms.
(4•2)•(10^4 • 10^-5 )
Multiply the numbers. Multiply the terms with the same base by adding their exponents.
8•10^4-5
Calculate the difference and you get 8•10^-1
Hope this helps ʕ•ᴥ•ʔ