Pro Tip: As you're reading a word problem such as this, you should be asking "How difficult would it be to test the answer choices?"

In this case, testing the answer choices is easy, since we're told that Bobby has eight more cars than Jackie
Also note that the question asks, "How many cars does Bobby currently have?"

A. 2. If Bobby has 2 cars, then that means Jackie has -6 cars (since Bobby has 8 more cars than Jackie). Eliminate A.
B. 4. If Bobby has 4 cars, then that means Jackie has -4 cars (since Bobby has 8 more cars than Jackie). Eliminate B.
C. 6. If Bobby has 6 cars, then that means Jackie has -2 cars (since Bobby has 8 more cars than Jackie). Eliminate C.
D. 8. If Bobby has 8 cars, then that means Jackie has 0 cars. Okay that could be the case. If Bobby gives 2 cars to Jackie, then Bobby will have 6 cars and Jackie will have 2 cars. HOWEVER, the question tells us that, After the exchange, Bobby will have TWICE the number of cars Jackie has. Eliminate D

No need to waste valuable time testing answer choice E, since we've already eliminated A, B, C and D.

Answer: E

Here's my analysis of answer choice E (for "fun")
E. 10. If Bobby has 10 cars, then that means Jackie has 2 cars (Since Bobby has 8 cars more than Jackie has). If Bobby gives 2 cars to Jackie, then Bobby will have 8 cars, and Jackie will have 4 cars. Perfect! After the exchange, Bobby will have TWICE the number of cars Jackie has. Everything checks out!