0=4.9t^2+8.4t+1.5

Solution for 0=4.9t^2+8.4t+1.5 equation:

0=4.9t^2+8.4t+1.5

We move all terms to the left:

0-(4.9t^2+8.4t+1.5)=0

We add all the numbers together, and all the variables

-(4.9t^2+8.4t+1.5)=0

We get rid of parentheses

-4.9t^2-8.4t-1.5=0

a = -4.9; b = -8.4; c = -1.5;
Δ = b2-4ac
Δ = -8.42-4·(-4.9)·(-1.5)
Δ = 41.16
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{-(-8.4)-\sqrt{41.16}}{2*-4.9}=\frac{8.4-\sqrt{41.16}}{-9.8}
$
$t_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(-8.4)+\sqrt{41.16}}{2*-4.9}=\frac{8.4+\sqrt{41.16}}{-9.8}
$