Suppose that we have disjoint normal populations A and B with equal but unknown population variances. Suppose we plan a sample of size 12 from from population A and a sample of size 6 from population...

Suppose that we have disjoint normal populations A and B with equal but unknown population variances.   Suppose we plan a sample of size 12 from from population A and a sample of size 6 from population B which we will pool to form the pooled variance.  If the sample variance for the sample from population A is 25 and the sample variance for the sample from population B is 36, then what is the pooled sample variance?