Kevin is an auto mechanic. He spends 2 hours when he replaces the shocks on a car and 2 hours when he replaces the brakes. He works no more than 42 hours a week. He routinely completes at least 4 shocks replacements and 6 brake replacements a week. If he charges $450 for labor replacing shocks and $300 in labor for replacing brakes, how many jobs of each type should he complete a week to maximize his income? Kevin should do I:I shock replacements and I:I brake replacements every week to maximize his weekly income