-0.05t^2+3.5t=60

Solution for -0.05t^2+3.5t=60 equation:

-0.05t^2+3.5t=60

We move all terms to the left:

-0.05t^2+3.5t-(60)=0

a = -0.05; b = 3.5; c = -60;
Δ = b2-4ac
Δ = 3.52-4·(-0.05)·(-60)
Δ = 0.25
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{-(3.5)-\sqrt{0.25}}{2*-0.05}=\frac{-3.5-\sqrt{0.25}}{-0.1}
$
$t_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(3.5)+\sqrt{0.25}}{2*-0.05}=\frac{-3.5+\sqrt{0.25}}{-0.1}
$