When you add a zero to the problem, it shows you are now multiplying in the double-digits. Let's say you are multiplying 12x12. First you cover up the one then multiply them. Then cover up the two and you have 10. When you multiply them, it ends in a zero. Don't think of it as adding a zero but adding to products.
A line is 180 degrees. I found the degree of the angles in-between 126 and M by subtracting 126 from 180. This means that M is also 126. (Plus the intersecting lines are parallel)
