81=-16t^2+93t+4

Solution for 81=-16t^2+93t+4 equation:

81=-16t^2+93t+4

We move all terms to the left:

81-(-16t^2+93t+4)=0

We get rid of parentheses

16t^2-93t-4+81=0

We add all the numbers together, and all the variables

16t^2-93t+77=0

a = 16; b = -93; c = +77;
Δ = b2-4ac
Δ = -932-4·16·77
Δ = 3721
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$t_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$t_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$\sqrt{\Delta}=\sqrt{3721}=61$
$t_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(-93)-61}{2*16}=\frac{32}{32}
=1
$
$t_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(-93)+61}{2*16}=\frac{154}{32}
=4+13/16
$