What letter, by convention, is used for a variable when another name isn’t obvious?

An automated water dispenser fills packets with one liter of water on average, with a standard deviation of 5 milliliter. the manual says that after a year of operation the dispenser should be tested to see if it needs recalibration. a year later a number of filled packets are set aside and measured separately. it is found that the average packet now contains about 0.995 liters. does the dispenser need calibration? explain your answer.

Glenda makes an online purchase for picture frames for $12.95 each and formats of $5.89 each the site says it taxes paid by the customer or 6.5% of the total purchase price shipping charges are based on the

Assume that y varies inversely with x. if y=1.6 when x=0.5 find x when y=3.2