Manny works 40 hours per week. He must work for his parents where he earns $8 per hour. He also works for a computer company where he earns $20 per hour. What is the minimum number of hours Manny can work for the computer company to earn a total of $464 per week from both jobs?

p + c = 40 ... 8 p + 8 c = 320

8 p + 20 c = 464

subtracting equations (to eliminate p) ... 12 c = 144

solve for c