15=-16t^2+30t+4

Solution for 15=-16t^2+30t+4 equation:

15=-16t^2+30t+4

We move all terms to the left:

15-(-16t^2+30t+4)=0

We get rid of parentheses

16t^2-30t-4+15=0

We add all the numbers together, and all the variables

16t^2-30t+11=0

a = 16; b = -30; c = +11;
Δ = b2-4ac
Δ = -302-4·16·11
Δ = 196
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$t_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$t_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$\sqrt{\Delta}=\sqrt{196}=14$
$t_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(-30)-14}{2*16}=\frac{16}{32}
=1/2
$
$t_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(-30)+14}{2*16}=\frac{44}{32}
=1+3/8
$