1510=75t+4.905t^2

Solution for 1510=75t+4.905t^2 equation:

1510=75t+4.905t^2

We move all terms to the left:

1510-(75t+4.905t^2)=0

We get rid of parentheses

-4.905t^2-75t+1510=0

a = -4.905; b = -75; c = +1510;
Δ = b2-4ac
Δ = -752-4·(-4.905)·1510
Δ = 35251.2
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{-(-75)-\sqrt{35251.2}}{2*-4.905}=\frac{75-\sqrt{35251.2}}{-9.81}
$
$t_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(-75)+\sqrt{35251.2}}{2*-4.905}=\frac{75+\sqrt{35251.2}}{-9.81}
$