25b^2-15b-9.75=0

Solution for 25b^2-15b-9.75=0 equation:

25b^2-15b-9.75=0

a = 25; b = -15; c = -9.75;
Δ = b2-4ac
Δ = -152-4·25·(-9.75)
Δ = 1200
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$b_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$b_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

The end solution:

$\sqrt{\Delta}=\sqrt{1200}=\sqrt{400*3}=\sqrt{400}*\sqrt{3}=20\sqrt{3}$
$b_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(-15)-20\sqrt{3}}{2*25}=\frac{15-20\sqrt{3}}{50}
$
$b_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(-15)+20\sqrt{3}}{2*25}=\frac{15+20\sqrt{3}}{50}
$