Boardwalk Parity Bets

A boardwalk arcade stall runs a game built around a single fair six-sided die. Two wagers are on offer. Wager 1: put down $4 on the roll landing even; a winning ticket pays $6 back in total. Wager 2: put down $6 on the roll landing odd; a win returns $9 in total. You can buy as many tickets of either type as you like. If your goal is to maximize expected profit, what is the right amount to wager?