-750=-4.9t^2-3t

Solution for -750=-4.9t^2-3t equation:

-750=-4.9t^2-3t

We move all terms to the left:

-750-(-4.9t^2-3t)=0

We get rid of parentheses

4.9t^2+3t-750=0

a = 4.9; b = 3; c = -750;
Δ = b2-4ac
Δ = 32-4·4.9·(-750)
Δ = 14709
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$t_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$t_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

The end solution:

$\sqrt{\Delta}=\sqrt{14709}=\sqrt{1*14709}=\sqrt{1}*\sqrt{14709}=1\sqrt{14709}$
$t_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(3)-1\sqrt{14709}}{2*4.9}=\frac{-3-1\sqrt{14709}}{9.8}
$
$t_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(3)+1\sqrt{14709}}{2*4.9}=\frac{-3+1\sqrt{14709}}{9.8}
$