That works out to $180k per employee. If average income per employee is $100k, at a 5% state income tax rate, it would take 36 years to make back the money.
Under the theory that Boston and MA bear zero costs. Which is certainly untrue.
There's the added costs for those additional people in terms of traffic congestion, schools, and other services. There's also the lack of a guarantee that GE will stay long enough, or that they won't demand an even bigger tax break when this one expires.