0=-4.9x^2+140x+15

Solution for 0=-4.9x^2+140x+15 equation:

0=-4.9x^2+140x+15

We move all terms to the left:

0-(-4.9x^2+140x+15)=0

We add all the numbers together, and all the variables

-(-4.9x^2+140x+15)=0

We get rid of parentheses

4.9x^2-140x-15=0

a = 4.9; b = -140; c = -15;
Δ = b2-4ac
Δ = -1402-4·4.9·(-15)
Δ = 19894
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:

$\sqrt{\Delta}=\sqrt{19894}=\sqrt{49*406}=\sqrt{49}*\sqrt{406}=7\sqrt{406}$
$x_{1}=\frac{-b-\sqrt{\Delta}}{2a}=\frac{-(-140)-7\sqrt{406}}{2*4.9}=\frac{140-7\sqrt{406}}{9.8}
$
$x_{2}=\frac{-b+\sqrt{\Delta}}{2a}=\frac{-(-140)+7\sqrt{406}}{2*4.9}=\frac{140+7\sqrt{406}}{9.8}
$