35=-3.75x^2+30x

Solution for 35=-3.75x^2+30x equation:

35=-3.75x^2+30x

We move all terms to the left:

35-(-3.75x^2+30x)=0

We get rid of parentheses

3.75x^2-30x+35=0

a = 3.75; b = -30; c = +35;
Δ = b2-4ac
Δ = -302-4·3.75·35
Δ = 375
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

The end solution:

$\sqrt{\Delta}=\sqrt{375}=\sqrt{25*15}=\sqrt{25}*\sqrt{15}=5\sqrt{15}$
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(-30)-5\sqrt{15}}{2*3.75}=\frac{30-5\sqrt{15}}{7.5}
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(-30)+5\sqrt{15}}{2*3.75}=\frac{30+5\sqrt{15}}{7.5}
$