Jim and Kirk are playing a card game where they trade chips. At the beginning of the game, Jim has four times as many chips as Kirk does. After Kirk wins the game, Jim gives Kirk 18 of his chips, at which point they now have the same number of chips. How many did Kirk have to begin with? (a) If j represents the original number of chips Jim had and k represents the original number of chips that Kirk had, then write an equation that models the amount of chips they originally had. Explain your equation.

(b) The equation j - 18 = k + 18 models the scenario after Kirk wins the game. Explain why.

(c) Determine how many chips both Kirk and Jim started with.