Why your 4w lights blink when the 4w is not workigin your 2001?
You can add and subtract any like terms. Since 8w, -4w, and 4w are all like terms, since 8, -4, and 4 all tell how many w's you have. This is the essentially same as saying "There are 8 apples, subtract 4 apples, and add 4 apples." (Don't forget that 8w-4w is the same as 8w + -4w). To solve, just add 8, subtract 4, and add 4. Leave w alone. The answer is 4w.