Actually it is neither.
The acu is applied to he attack to determine how much of the attack is actually used.
So it would be:
1 Bil * .75 = 750 Mil
The acu bonus is applied to the acu by adding a percentage to it so it would be:
1 Bil * (.75*1.20) = 900 Mil
Can I tag on this thread and ask 2 more questions?
Would the above explanation apply to hitpoint and shield bonus?
A sample ---------
1,000,000,000 hitpoints, 70% absorbing shield, with 10% Special Alloy bonus and 5% shield bonus.
1,000,000,000 hp with 70% shield yields 1,700,000,000 hp.
Add on to it the 10% and 5% means 1,700,000,000 X 1.1 X 1.05 = 1,963,500,000 hp.
Is that correct?