Hi, 150 came from the way they multiplied it, the organization of multiplying, let me demonstrate:
15 * 12 =
you first multiply out by 2 and get 30then you multiply out by 1 but you have to indent your numbers so:
30
+ 15
------
180
They just added 0 to the last place after 5 to keep things in order, that 0 doesn't have to be there but you can add it.
