-8.5=6.7t-4.9t^2

Solution for -8.5=6.7t-4.9t^2 equation:

-8.5=6.7t-4.9t^2

We move all terms to the left:

-8.5-(6.7t-4.9t^2)=0

We get rid of parentheses

4.9t^2-6.7t-8.5=0

a = 4.9; b = -6.7; c = -8.5;
Δ = b2-4ac
Δ = -6.72-4·4.9·(-8.5)
Δ = 211.49
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{-(-6.7)-\sqrt{211.49}}{2*4.9}=\frac{6.7-\sqrt{211.49}}{9.8}
$
$t_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(-6.7)+\sqrt{211.49}}{2*4.9}=\frac{6.7+\sqrt{211.49}}{9.8}
$