First add the whole numbers.
Then find the LCM (least common multiple) of 3 and 2, which are the denominators of both fractions. In this case, the LCM of 3 and 2 are 6.
As you can see in the photo, I multiplied a number than can result in 6 in both denominators. Then multiply that same number to the numerators.
Finally, add 21+2, but keep the denominator as 6.
This is how I learned it, hope it helps.
