A d⁸ ion has Δo = 102 kJ/mol with a certain ligand…

Step 1. Octahedral. $\text{CFSE} = (-0.4 \times 6 + 0.6 \times 2) \times 102 = -1.2 \times 102 = -122.4\ \text{kJ/mol}$.

Step 2. The tetrahedral splitting. $\Delta_t = \tfrac{4}{9} \times 102 = 45.3\ \text{kJ/mol}$.

Step 3. Tetrahedral. $\text{CFSE} = (-0.6 \times 4 + 0.4 \times 4) \times 45.3 = -0.8 \times 45.3 = -36.3\ \text{kJ/mol}$.

Step 4. Preference. $122.4 - 36.3 = 86.1\ \text{kJ/mol}$.