-(.2t^2-20t+375)=0

Solution for -(.2t^2-20t+375)=0 equation:

-(.2t^2-20t+375)=0

We get rid of parentheses

-.2t^2+20t-375=0

We add all the numbers together, and all the variables

-0.2t^2+20t-375=0

a = -0.2; b = 20; c = -375;
Δ = b2-4ac
Δ = 202-4·(-0.2)·(-375)
Δ = 100
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$t_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$t_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$\sqrt{\Delta}=\sqrt{100}=10$
$t_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(20)-10}{2*-0.2}=\frac{-30}{-0.4}
=+75
$
$t_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(20)+10}{2*-0.2}=\frac{-10}{-0.4}
=+25
$