-3t(5-t)=18

Solution for -3t(5-t)=18 equation:

-3t(5-t)=18

We move all terms to the left:

-3t(5-t)-(18)=0

We add all the numbers together, and all the variables

-3t(-1t+5)-18=0

We multiply parentheses

3t^2-15t-18=0

a = 3; b = -15; c = -18;
Δ = b2-4ac
Δ = -152-4·3·(-18)
Δ = 441
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$t_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$t_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$\sqrt{\Delta}=\sqrt{441}=21$
$t_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(-15)-21}{2*3}=\frac{-6}{6}
=-1
$
$t_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(-15)+21}{2*3}=\frac{36}{6}
=6
$