Pre-acquisition standalone values:

ABB = $55m

BBA = $25m

Total pre-deal value = $80m.

After the acquisition, ABB (the combined business) is expected to generate post-tax cash flows of $10m per year in perpetuity. Cost of equity = 10%, and the firm is all-equity financed, so:

Post-acquisition value=100.10=$100m\text{Post-acquisition value} = \frac{10}{0.10} = \$100\text{m}Post-acquisition value=0.1010​=$100m

Synergy value = value of combined firm − sum of standalone values:

Synergy=100−80=$20m\text{Synergy} = 100 - 80 = \$20\text{m}Synergy=100−80=$20m

So the best estimate of the synergy from the acquisition is $20 million.