Answer:
521.
Step-by-step explanation:
143
+ 378
= 521
Working from right to left:
First add the 3 and 8 = 11
write 1 underneath
and carry the other 1 to the second column.
1 +4+7 = 12. Write 2 and carry the 1 to the first column.
1 + 3 + 1 = 5.
Answer 521.
