678 + 303 = 981
Here are a few examples to get you started:
600 + 300 = 900
78 + 3 = 81
900 + 81 = 981
Here's another one:
678 = 600 + 70 + 8
303 = 300 + 00 + 3
Add the ones place = 11
Add the tens place = 70
Add the hundreds place = 900
Now add 900 + 70 + 11 = 981
Hope this helps! :-)