Answer: plan A
Explanation:
plan A: 
 $500 - $180 = $320 remaining --> $320 ÷ $40 per week = 8 weeks
 You would be paying $40 for 8 weeks to fully pay off the Playstation.
plan B: 
 $500 ÷ $50 per week = 10 weeks
 You would be paying $50 for 10 weeks to fully pay off the Playstation.