P(x)=60x-0.4x^2-4x+15

Solution for P(x)=60x-0.4x^2-4x+15 equation:

(P)=60P-0.4P^2-4P+15

We move all terms to the left:

(P)-(60P-0.4P^2-4P+15)=0

We get rid of parentheses

0.4P^2-60P+4P+P-15=0

We add all the numbers together, and all the variables

0.4P^2-55P-15=0

a = 0.4; b = -55; c = -15;
Δ = b2-4ac
Δ = -552-4·0.4·(-15)
Δ = 3049
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$P_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$P_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$P_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(-55)-\sqrt{3049}}{2*0.4}=\frac{55-\sqrt{3049}}{0.8}
$
$P_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(-55)+\sqrt{3049}}{2*0.4}=\frac{55+\sqrt{3049}}{0.8}
$