The PMBOK lists for EAC:

EAC = AC + Bottoms Up ETC (per PMBOK, this is the most common in real life) Use if initial estimate is flawed

EAC = BAC/CPI Use if you are continuing with the same cost efficiency (any variances will continue) Per the internet, this is the most common formula used for test answers

EAC = AC + (BAC - EV) Use if any variances you have experienced will not occur again, and you will continue at the planned aka budgeted rate

EAC = AC ((BAC=EV)/CPI * SPI)) Use if you have a schedule goal or constraint.