Verified answer

y = -3x^2 + 15x

or, y=-3(x^2-2*(5/2)x+(5/2)^2)+3*(5/2)^2

or, y-75/4 = -3(x-(5/2))^2

y = - 3 ( x ² - 5 x )

y = - 3 ( x ² - 5x + 25/4 ) + 75/4

y = - 3 ( x - 5/2 ) ² + 75/4

y - 75/4 = - 3 ( x - 5/2 ) ²