He made an error on the second line. Kurt didn't distribute the 3 to each term inside the parenthesis of (x-7)
3(x-7) does not turn into 3x-7. Instead, it should be 3x-21 because 3*7 = 21.
This is what his steps should look like
3(x-7) = 2x - 14
3x - 21 = 2x - 14
3x-2x = -14+21
x = 7
