Question 973496
-3/2m^2+20m+17

The vertex m value (date) is at -b/2a. That is -20/-3 = +6.67 (June 20)
At that time the temperature maximum is -1.5(400/9)+1200/9 +17= (600/9)+17=83.33 degrees.

-1.5 m^2 + 20 m -63 =0, moving 80 to the left

1.5^m^2 - 20 m +63=0

(1/3) * [20 +/- sqrt (400-378)]  = (1/3) [20 +/- sqrt 22]   sqrt 22=4.69
(1/3) 24.69=8.23   August 7
(1/3) 15.31=5.10   May 3

{{{graph (300,300,-1,15,-5,95,(-3/2)x^2+20x+17)}}}