18=4+31t-16t2

Solution for 18=4+31t-16t2 equation:

18=4+31t-16t^2

We move all terms to the left:

18-(4+31t-16t^2)=0

We get rid of parentheses

16t^2-31t-4+18=0

We add all the numbers together, and all the variables

16t^2-31t+14=0

a = 16; b = -31; c = +14;
Δ = b2-4ac
Δ = -312-4·16·14
Δ = 65
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{-(-31)-\sqrt{65}}{2*16}=\frac{31-\sqrt{65}}{32}
$
$t_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(-31)+\sqrt{65}}{2*16}=\frac{31+\sqrt{65}}{32}
$