Reading 34 EOC #1 Increase Interest Expense -> Change in FCFF

CFA Level II Equities
#1

According to the solution, $100 increase in interest expense resulted in 0 change in FCFF.

But FCFF = NI + NCC + Int(1-tax) - FCInv - WCInv

Shouldn’t FCFF increase by 100*(1-tax)??

#2

If you increase your interest expense by $100, your NI will be lower, by the amount you’re adding back anyway. So net net, no change