Work Step by Step
First, add the digits in the ones place. Since $7+3=10$, you have to "carry the one" to the tens place, and fill the ones place with a 0. When you add the digits in the tens place, you have to remember to also add the one that was carried over. $8+6+1=15$, so the final answer is 150. This matches the answer that was given in the book.