How to find the column of the last "X" in my table

For one of my homework, I have to calculate multiple things on this table with only Excel formula. One of the things that I have to calculate is the opening time (how long this place is open) and because there's sometimes multiple X in a columns or it doesn't alwalys start at 8am (8h) and close at 5pm (17h), so I can't just count all the X or smthg like that...
So I tought that I could just find the columns of the first and last X and just compare them after but I can't manage to find a formula that give me the columns of the last X...
To find the columns of the first X, I use this :
=ROUNDUP(match("X";flatten(transpose(G24:AT30));0)/7;0)
Someone can help me for the formula that find find the columns of the last X ?
(remember : you can just use formula in one cell, so you can't rewrite the table somewhere else for exemple)