How did he get his answer 0.51???
"A is a multiple of B", where A and B are integers, means that there exist some integer C such that A= BC.
6 is a multiple of 6 because it is equal to 1(6). That is, C= 1. 12 is multiple of 6 because 12= (6)(2). It is the "1" and "2" that causes them to say "first" multiple and "then". The next few multiples are 3(6)= 18, 4(6)= 24, 5(6)= 30, etc.