There aren't enough equations to solve it, I think, but ...

If you just combine the numbers:

1712 x 60% + 56 x 30% + 21 x 10% = 1027.2 + 16.8 + 2.1 = 1046.1

1112 x 60% + 36 x 30% + 22 x 10% = 667.2 + 10.8 + 2.2 = 680.2

Then we could have:

f(x) = y

f(1046.1) = 21.4

f(680.2) = 35.7

The function f(x) in this case **could be**: 35.7 - (x-680.2)*(14.3/365.9)

So, when x = 1046.1, then y = 35.7 - (1046.1-680.2)*365.9 = 35.7 - (1046.1-680.2)*(14.3/365.9) = 35.7 - 14.3 = 21.4

And, when x = 680.2, then y = 35.7 - (680.2-680.2)*365.9 = 35.7 - 0 = 35.7

But I don't know how to treat the X, Y and Z separately. If you had a few more equations, we could maybe do a better job.