First, compute ma$(x, y, z) = \frac{1}{2}[\text{le}(15, 10, 9) + \text{la}(15, 10, 9)]$.
le$(15, 10, 9) = \max(15-10, 10-9) = \max(5, 1) = 5$.
la$(15, 10, 9) = \min(15+10, 10+9) = \min(25, 19) = 19$.
So ma$(15, 10, 9) = \frac{1}{2}(5 + 19) = \frac{24}{2} = 12$.
Now compute le$(9, 8, 12) = \max(9-8, 8-12) = \max(1, -4) = 1$.
Next, $\min(y, x - z) = \min(10, 15 - 9) = \min(10, 6) = 6$.
Finally, le$(15, 6, 1) = \max(15 - 6, 6 - 1) = \max(9, 5) = 9$.
Wait — the calculation needs check:
We have le$(x, \min(y, x-z), \ \text{le}(9, 8, \text{ma})) = \text{le}(15, 6, 1) = \max(15 - 6, 6 - 1) = \max(9, 5) = 9$.
This yields option (c) instead of (a).