He moved the decimal to the right 4 times. He should of moved it to the right 2 times. Giving him 0.15%
3(k-x)= -3x-9
3k - 3x = -3x - 9 ← equation without parentheses
3k - 3x + 3x = - 9
3k = -9
k = -9/3
k = -3 ← simplest form
Need a little bit more information to be able to answer the question