25=-4.9x^2+30x+4

Solution for 25=-4.9x^2+30x+4 equation:

25=-4.9x^2+30x+4

We move all terms to the left:

25-(-4.9x^2+30x+4)=0

We get rid of parentheses

4.9x^2-30x-4+25=0

We add all the numbers together, and all the variables

4.9x^2-30x+21=0

a = 4.9; b = -30; c = +21;
Δ = b2-4ac
Δ = -302-4·4.9·21
Δ = 488.4
The delta value is higher than zero, so the equation has two solutions
We use following formulas to calculate our solutions:
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}$

$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(-30)-\sqrt{488.4}}{2*4.9}=\frac{30-\sqrt{488.4}}{9.8}
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(-30)+\sqrt{488.4}}{2*4.9}=\frac{30+\sqrt{488.4}}{9.8}
$