Hey Chris! This is Chris D., a senior in high school. I couldn`t really tell you if your teacher`s calculations are correct. But he/she has the correct idea. This scenario might help you understand a little better.
Let`s say You are in a spacecraft that is flying by earth at the speed of light. Your sister is on earth watching you and a clock you have in the ship. To you, as you get closer to moving at the speed of light, there will feel like no change and the clock will keep ticking like usual. To your sister, as your speed increases, the second hand on your clock will slow down. When you reach the speed of light, she will see that you and the clock(not the ship,but the things inside) will have completely stopped! While are at the speed of light, she we grow old and die, yet she will see no change at all in your clock. What you would see, I have no idea, but I can theorize just as good as you.

I`m sorry this message is sooo long, but I hoped I answered your question.