25=4.9t^2+25t

Solution for 25=4.9t^2+25t equation:

25=4.9t^2+25t

We move all terms to the left:

25-(4.9t^2+25t)=0

We get rid of parentheses

-4.9t^2-25t+25=0

a = -4.9; b = -25; c = +25;
Δ = b2-4ac
Δ = -252-4·(-4.9)·25
Δ = 1115
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$t_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$t_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$t_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(-25)-\sqrt{1115}}{2*-4.9}=\frac{25-\sqrt{1115}}{-9.8}
$
$t_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(-25)+\sqrt{1115}}{2*-4.9}=\frac{25+\sqrt{1115}}{-9.8}
$