12 + 42 is 54. If you take the numbers apart and add them into tens. 42 because 4 10s and your left with 2 ones. If you take 12 and seperate it into tens you get 1 ten with a remainder of 2. 10 + 10 + 10 + 10 + 10 = 50. 2+2 is 4. Remember that they are the same number so 50 + 4 is 54.
