0=140-(0.5)(9.8)t^2

Solution for 0=140-(0.5)(9.8)t^2 equation:

Simplifying
0 = 140 + -1(0.5)(9.8) * t2

Multiply -1 * 0.5
0 = 140 + -0.5 * 9.8t2

Multiply -0.5 * 9.8
0 = 140 + -4.9t2

Solving
0 = 140 + -4.9t2

Solving for variable 't'.

Move all terms containing t to the left, all other terms to the right.

Add '4.9t2' to each side of the equation.
0 + 4.9t2 = 140 + -4.9t2 + 4.9t2
Remove the zero:
4.9t2 = 140 + -4.9t2 + 4.9t2

Combine like terms: -4.9t2 + 4.9t2 = 0.0
4.9t2 = 140 + 0.0
4.9t2 = 140

Divide each side by '4.9'.
t2 = 28.57142857

Simplifying
t2 = 28.57142857

Take the square root of each side:
t = {-5.345224838, 5.345224838}