How many teachers?

Again, the MNEA voted on incentive pay. The Tennessean reports:

Members of the Metropolitan Nashville Education Association voted 70 percent to 30 percent to participate in the $10 million scientific study, in conjunction with Vanderbilt University's new National Center on Performance Incentives.

My question is how many is 70% and 30%? How many of the 4,983+- teachers employed by Metro and how many of the MNEA membership got to decide whether these 300 teachers would be allowed to participate in this study? Was the voting process improved after they rejected the NAPE project? Or was that unnecessary since the MNEA had already made it clear they were for this version?