Calculate the Sum: 4 + 9 + 8 Addition Problem

Let's break down 4 into a smaller addition problem:

$3+1$

Now we'll get the exercise:

$3+1+9+8=$

Since the exercise only involves addition, we'll use the commutative property and start with the exercise:

$1+9=10$

Now we'll get the exercise:

$3+10+8=$

Let's solve the exercise from right to left:

$10+8=18$

$18+3=21$