Some research has suggested that teacher performance may not improve with more experience. You acquire data on test scores of particular classes and regress test scores on various control variables and the years of experience of the teacher and the years of experience squared. The coefficient on experience is 60; on experience squared it is -0.4. Calculate the point at which teacher experience goes from having a positive to a negative effect on test scores. Do your data support the conclusion that at some point, more teacher experience reduces test scores?

report your answers with one decimal place (e.g. 6.1)