What is the second x of 3x-5y=20

I'll give brainliest if you answer right : )

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 axis of symmetry of the function f(x)=-(x+ 9)(x-21)