**for part (b) : a + b + a + b**

DAG is :

and Value number table will be:

1 ID | a | |

2 ID | b | |

3 + | 1 | 2 |

from this we conclude that :

the value number of + is 3 and its left child has 1 and right child has 2

**Is this correct value number table and DAG for (b)? correct me if i am wrong?**