I'm completely new to Mathematica, and I'm facing an issue.

[![enter image description here](https://i.stack.imgur.com/JQJQz.png)](https://i.stack.imgur.com/JQJQz.png)

So basically, I know that Out[43]'s answer is 1+2a+3b. And out[44] is a+b. I dont know why it's giving me a different answer here. Can anyone help? Thank you!!