Explain how multiplying with 6 is like multiplying with 3

Well 6 is the double of 3 (2 times 3 equals 6)
So for example: 6 times 2 equals 12 could also be written 3 times 2 times 2 equals 12.
Either way is correct but 6 times 2 is a lot easier and quicker than 3 times 2 times 2. :) hope that answers your question

Technically since it's half of six , you can multiply it back to 6 , which you can basically get the same multiplication on any number 6 can for example --- 6×7=42 and 3×14=42