Increasing/decreasing; Rate Of Decrease - Spreadsheet

I’m trying to make this:

Amount of money: 1000 (changeable)
Beginning # of units: 0,1 (changeable)
Delta: 200 (changeable)
Rate of decrease: 50% (changeable)

0,1 unit should be added for every 200$ increase (1000+200=1200; 1200+200=1400; 1400+500=1900; 1900+256=2156 etc)
0,1 unit should be taken away after decreasing by100$ (because the rate of decrease = 50% (changeable))

After increasing of 1000 + 200, quantity of units should also increase for 0,1, so it should be 0,2 (1200), 0,3(1400), 0,4(1600)….. Amount of money can increase not only by 200, but for any sum. If that sum is (for example) 500, we should increase by 0,2 etc.

But when this some decreasing we are using rate of decrease (for example 50%, (changeable):
0,4 units – 1600
0,3 units – 1500
0,2 units – 1400
0,1 unit – 1300