Well, this is more a mathematical problem than a programming one, isn't it.
To begin, you have an inner width of 220px inside a div of 200px, aligned left. Your offset is then 10px (half the difference). You need to move the center of the inner div 10px to the left to get it centered.
Then. you are applying a scale of 0.75. That means a delta (or change) of 0.25. To get a delta of 10px (the movement that you need), you have to apply it to 40px of initial length (10px divided by 0.25). If your transform is happening 40px to the left of the center of the inner div, it will center it.
Now, since the center is at 110px from the left edge, this point 40px to the left of the center is 70px to the right of the left edge.
And finally, 70px in a 220px width is 31.81 %.
Try it and you will see