48=23d+2.3d^2

Solution for 48=23d+2.3d^2 equation:

48=23d+2.3d^2

We move all terms to the left:

48-(23d+2.3d^2)=0

We get rid of parentheses

-2.3d^2-23d+48=0

a = -2.3; b = -23; c = +48;
Δ = b2-4ac
Δ = -232-4·(-2.3)·48
Δ = 970.6
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$d_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$d_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$d_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(-23)-\sqrt{970.6}}{2*-2.3}=\frac{23-\sqrt{970.6}}{-4.6}
$
$d_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(-23)+\sqrt{970.6}}{2*-2.3}=\frac{23+\sqrt{970.6}}{-4.6}
$