48=-16t^2+56t

Solution for 48=-16t^2+56t equation:

48=-16t^2+56t

We move all terms to the left:

48-(-16t^2+56t)=0

We get rid of parentheses

16t^2-56t+48=0

a = 16; b = -56; c = +48;
Δ = b2-4ac
Δ = -562-4·16·48
Δ = 64
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$t_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$t_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$\sqrt{\Delta}=\sqrt{64}=8$
$t_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(-56)-8}{2*16}=\frac{48}{32}
=1+1/2
$
$t_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(-56)+8}{2*16}=\frac{64}{32}
=2
$