The notation E x 1 must mean the n x n matrix in which each column is equal to E. Then the i'th element of (E x 1)R' will be the i'th element of E times the sum of the elements of R'. But ||R'||_1 = 1 (and presumably the elements of R' are non-negative), so the sum of the elements of R' is 1. Therefore (E x 1)R' = E.