How do i find the slope of a line? ?

What is the value of x in the diagram below?

The given dot plot represents the average daily temperatures, in degrees fahrenheit, recorded in a town during the first 15 days of september. if the dot plot is converted to a box plot, the first quartile would be drawn at __ , and the third quartile would be drawn at link to the chart is here

What is the solution to this system of equations? y= 2x - 3.5 x - 2y = -14