Two-digit numbers can be multiplied by lining up the ones value and the tens value and summing the vertical lines. If a two-digit number is multiplied by a one-digit number, then the ones value and the tens value are summed separately and the former is added after the latter.
As an example, when multiplying 23 by 3, once the numbers are lined up the two equations are 3 times 3 for the ones value and 3 times 2 for the tens value. The first equation gives an answer of 9, while the second results in 6. However, the 6 is actually 60 because it is the answer from the tens column. Once this is done, 6 and 9 can be joined together to make 69.