Alli has hired mark and alexis to work for his shipping company. mark can load a truck with packages in 120 minutes. alexis can load the same number of packaged in 240 minutes. if mark and alexis work together on a particular truck, how many minutes will it take them to load all of the packages

Atennis club charges a monthly membership fee of $150 and charges it members $10 per hour to use a court. there's also $500 fee to become a member. stella joined the tennis club last spring, and she has been a member for 5 months. she has been playing 10 hours of tennis each month. stella values an hour of her time at $20. during a boring afternoon meeting, stella thinks about reserving a court to work on her serve for an hour tonight. what's stella's opportunity cost of working on her serve for an hour?