robiripper

First of all, I'm totally new to this game. I've played the Call of Duty series of games with no problem and someone mentioned ARMA 3. I previewed the game and was hooked. I just bought this game, I heard it was difficult but gimme a BRAKE ! In the first interactive scenario ( COMMON DENOMINATOR ), the team leader tells me "Go to the crate and take out the "RCO". I face the crate, hit the [ I ] key, INVENTORY pops-up. There are 2 boxes, one on the Left (GROUND/CRATE), on the Right are slots for my gear. The (MX 6.5mm) RIFLE slot clearly shows where you're supposed to mount the "RCO" scope. Next, click on the "RCO" on the left and DRAG it to the scope mounting bracket highlighted in white on top of the receiver. Simple, right ? WROOOONG ! For 2+ days now I have DRAGGED and DROPPED, over and over. I've read the FIELD MANUAL a gazillion times, scoured the web and have come up with ZERO ! I tried using a KB/M, Xbox One Controller and KB w/built-in mouse pad and NOTHING WORKS. Does ANYONE have a clue how to fix this ? If so, PLEASE let me know. Thank you.