39 x 5 = (30 x 5) + (9 x 5) = 150 + 45 = 195
He did not change the sign of operation when 28 crossed the equals sign.
Add like terms
-4x+x=-3x
6-2=4
So the simplified term is 4-3x
The equation only is true for objects with negligible air resistance. A feather does not have this property.
Using the equation shown:
50 = -16t^2
t^2 = 50/16 = 3.125
t = sqrt(3.125) = 1.77 seconds
