Sum-Things Missing Puzzle - Solution

The Puzzle:

An old Mathematics book contained this addition sum which had been marked correct by the teacher:

The three squares in the diagram are where the paper was so bad I couldn't read them.

What were the three missing numbers?

The most obvious place to start was the 0 on the bottom (don't forget to carry the 1!).

Working towards the left, the next one has to be 9 to make the total 16 (+1 = 17) so we carry another 1.

That means the top left digit must be empty (or a zero):

Puzzle Author: Stephen Froggatt