I have a row of cells some of which are populated with an "x". I am looking
for a function that will tell me the first blank cell in a row. For example,
see below. I want to put a formula in column B that says, "find the first
blank cell in the row and return the task number. In cell B2 the return
should be E1 (or "3" indicating that John is currently on task 3). In cell
B3 the return should be D1 (or "2" indicating that Joe is on task 2).

A B C D E F
1 Task 1 2 3 4
2 John X X
3 Joe X
4 Martha X X X

The actual spreadsheet that I am working with is far more complicated but
this is generally what I am trying to accomplish. Can anyone help?

Thanks