-50=2.1t-1.25t^2

Solution for -50=2.1t-1.25t^2 equation:

-50=2.1t-1.25t^2

We move all terms to the left:

-50-(2.1t-1.25t^2)=0

We get rid of parentheses

1.25t^2-2.1t-50=0

a = 1.25; b = -2.1; c = -50;
Δ = b2-4ac
Δ = -2.12-4·1.25·(-50)
Δ = 254.41
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{-(-2.1)-\sqrt{254.41}}{2*1.25}=\frac{2.1-\sqrt{254.41}}{2.5}
$
$t_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(-2.1)+\sqrt{254.41}}{2*1.25}=\frac{2.1+\sqrt{254.41}}{2.5}
$