Question

How to solve y = -0.04x^2 + 1.3x + 56 using the quadratic formula?

Answer 1

Solve? You mean the zeroes?
y=0=-0.04x^2 + 1.3x + 56

x=(1.3 +-sqrt(1.3^2+3*.04*56)/(.08)

do the math.

Answer 2

Do you mean 4*0.4? And how did you get positive 0.4? That was the part that confused me.