If variances had been atypical then you would use EAC = AC + (BAC – EV) where you do not have enough information. Note that for typical variances EAC = BAC/CPI is another simplified version of EAC = AC + (BAC-EV)/CPI. Just develop the second formula to EAC = AC + BAC/CPI – EV/CPI. Knowing that AC=EV/CPI, you get to EAC = AC + BAC/CPI – AC or again EAC = BAC/CPI.