I cannot manage it without more refractors

Make rectangle inside the box where the lasers are towards the right. (In other words, make both lasers meet.) Then with one of the double mirror angle it were it sends a beam in both directions out of the box, start building a slanted rectangle towards the left side. after that, you should have two mirrors and one double mirror left.

Do the same thing with the double mirror you have left To the slanted rectangle. The remaining two mirrors should be no problem to place.

If you need a pic. let me know I just need to remember how to make it small enough to send. Always forget how to do that.

Hope this helps

Many thanks Gllo21 for the prompt reply, which
unfortunately is no help at all because I have only 10
ordinary mirrors and two refractors. Not a double mirror
in sight. No wonder I couldn't get it to work.
This is my first use of the forum. Not your fault it is
unsuccessful. Joss

Use the refractors instead of the double mirrors, (my bad) I called them wrong. Four mirrors are to do the inside and four to do the outside rectangles and the last two are to aim them at the coins.

The inside refractor will will refract them at an angle and the ouside refractor straight. heres the pic.

Success ! Thankyou. I managed without the picture, but
I think I would never have done so without your advice.
I suspect that I will be making a lot of use of the Forum in
the future, so maybe I'll using more of your help. Joss

Glad to read that you got it. I get grey hair with some of them. But, that's the good thing about this game, it makes you think like crazy.