I'm sure that I've just been looking at this stuff too long but I cannot understand how the answer was achieved?

Javier is completing his final project report.  He includes information on the final variances.  If the project was scheduled to take 12 months and it finishes in 14 months, what would Javier's final SPI results be?

a) 1

b) 1.17

c) 0.86

d) Not enough information to determine.  

The answer is 1, but it's not clear to me why.  Can anyone explain?