B= [2 8 .6 3 ] a= 3 0 2 -1] what is ba ?

The dot product of two vectors is defined as the sum of the multiplication of each of its components.
 We have then:
 B = [2 8 .6 3]
 A = [3 0 2 -1]
Making the product point:
 BA = [2 8 .6 3] [3 0 2 -1]
 BA = (2 * 3) + (8 * 0) + (0.6 * 2) + (3 * (- 1))
 BA = 4.2
 Answer
 BA = 4.2