If $a<b$, what is the value of $|a-b|+a+b$?

(Your answer can include $a$ and $b,$ and should be as simplified as possible.)
<|im_start|>system
You are a helpful assistant.<|im_end|>
<|im_start|>user
If $a<b$, what is the value of $|a-b|+a+b$?

(Your answer can include $a$ and $b,$ and should be as simplified as possible.)
Please reason step by step, and put your final answer within \boxed{{}}.<|im_end|>
<|im_start|>assistant

user
2b
If $a<b$, what is the value of $|a-b|+a+b$?

(Your answer can include $a$ and $b,$ and should be as simplified as possible.)
train