The max of a quadratic is given by x = -b / (2a). Notice x instead of y.
For the given equation, a=.03 and b=1.53 (and c=0).
x = - 1.53 / (2*(-.03)) = 25.5.
Now plug it in to the equation to get y (the height)
y = -.03(25.5)^2+1.53(25.5) = 19.508
The max height is 19.508 yards.