0=-4.9t^2+75t

Solution for 0=-4.9t^2+75t equation:

0=-4.9t^2+75t

We move all terms to the left:

0-(-4.9t^2+75t)=0

We add all the numbers together, and all the variables

-(-4.9t^2+75t)=0

We get rid of parentheses

4.9t^2-75t=0

a = 4.9; b = -75; c = 0;
Δ = b2-4ac
Δ = -752-4·4.9·0
Δ = 5625
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$t_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$t_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$\sqrt{\Delta}=\sqrt{5625}=75$
$t_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(-75)-75}{2*4.9}=\frac{0}{9.8}
=0
$
$t_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(-75)+75}{2*4.9}=\frac{150}{9.8}
=15+1/3.26666666667
$