Trying to write an If statement that will show date of last item selected and change as updated

I have a series of data. That goes down the left side column of dates... 8/2, 8/3, and such. Then 2 columns over I have a column left for if the date is checks so 8/2:X, 8/3:X, 8/4: ,8/5: and such. I'm wanting to reference the date in the last field that has a X in it

A B C D 8/1 X 8/2 X 8/3 x 8/4 8/5

Trying to reference the date for the last A cell if there is an X in the D cell. So it would be for 8/3 would be the date. I'm not sure how to run with this.

I've looked through but now sure how to state an if statement