5=8t-1.4t^2

Solution for 5=8t-1.4t^2 equation:

5=8t-1.4t^2

We move all terms to the left:

5-(8t-1.4t^2)=0

We get rid of parentheses

1.4t^2-8t+5=0

a = 1.4; b = -8; c = +5;
Δ = b2-4ac
Δ = -82-4·1.4·5
Δ = 36
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$t_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$t_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$\sqrt{\Delta}=\sqrt{36}=6$
$t_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(-8)-6}{2*1.4}=\frac{2}{2.8}
=1/1.4
$
$t_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(-8)+6}{2*1.4}=\frac{14}{2.8}
=5
$