Answer
$18+11=29$
$18
+11=
29$
Adding vertically is an easier way of calculating.
Work Step by Step
First, add the digits in the ones column (each number's ones place) to determine the digit in the ones place of the sum: $8+1=9$
Next, add the digits in the tens column (each number's tens place) to determine the digit in the tens place of the sum: $1+1=2$
If the sum has $2$ in the tens place and $9$ in the ones place, it must be $29$.