0=(15)t-4.905t^2

Solution for 0=(15)t-4.905t^2 equation:

0=(15)t-4.905t^2

We move all terms to the left:

0-((15)t-4.905t^2)=0

We add all the numbers together, and all the variables

-(15t-4.905t^2)=0

We get rid of parentheses

4.905t^2-15t=0

a = 4.905; b = -15; c = 0;
Δ = b2-4ac
Δ = -152-4·4.905·0
Δ = 225
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$t_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$t_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$\sqrt{\Delta}=\sqrt{225}=15$
$t_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(-15)-15}{2*4.905}=\frac{0}{9.81}
=0
$
$t_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(-15)+15}{2*4.905}=\frac{30}{9.81}
=3+0.57/9.81
$