Question

what is that value of the underline digit

Answer 1

Looking at the 429.  The value is 4 hundred.

Answer 2

It is listed as a whole number so there are three places it can be.

First it can be  in the ones place which is held by the nine.

Second it can be in the tens place which is held by the two.
 
And lastly it can be in hundreds place which is held by four.

The underlined number is four and is in the hundreds