How would i solve this by elimination

Kelly is a salesperson at a shoe store, where she must sell a pre-set number of pairs of shoes each month. at the end of each work day the number of pairs of shoes that she has left to sell that month is given by the equation s=300-15x , where s is the number of pair of shoes kelly still needs to sell and x is the number of days she has worked that month. what is the meaning of the number 300 in this equation

How can you find the mean absolute deviation (mad) for this set of data?

The random variable x is defined as the number marking the sector in which the arrow lands when the spinner in the diagram is spun once.