Image resizing & constrained aspect ratio

I need help. I have an image that needs to be resized to 200W, 150H. I uncheck constrain proportions box and it seems to work but colleagues are telling me the photo looks squashed and the constrained proportions box needs to be checked. But when I do check it, I cannot control the W and H. Then I was told to use the marquee tool to crop it and make the constrained aspect ratio 4x3 - how do I do this? I don't see anything called the constrained aspect ratio and cannot find it in the help area.
thanks in advance

Select rectangular marquee.
There are options at top of screen.
Under Style: Fixed Aspect ration
Put 4 and 3 in the other boxes.

Yep, the way you were doing it, you WERE "squashing" the image.

Mac

Oh, last step after making your 4x3 crop is Image/Crop.

Mac

Excellent. I can get it rightnow. thanks so much