0=15x-2.5x^2

Solution for 0=15x-2.5x^2 equation:

0=15x-2.5x^2

We move all terms to the left:

0-(15x-2.5x^2)=0

We add all the numbers together, and all the variables

-(15x-2.5x^2)=0

We get rid of parentheses

2.5x^2-15x=0

a = 2.5; b = -15; c = 0;
Δ = b2-4ac
Δ = -152-4·2.5·0
Δ = 225
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$\sqrt{\Delta}=\sqrt{225}=15$
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(-15)-15}{2*2.5}=\frac{0}{5}
=0
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(-15)+15}{2*2.5}=\frac{30}{5}
=6
$