Substituting cos B = -1/3 into the given expression, we get:

7cos(π + B) -2sin(π/2+B)

= 7cos(π)cos(B) - 7sin(π)sin(B) - 2sin(π/2)cos(B) - 2cos(π/2)sin(B)

= 7(−1)(−1/3) - 7(0)(sin(B)) - 2(0)(-1/3) - 2(1)(sin(B))

= 7/3 + 0 + 0 - 2sin(B)

= 7/3 - 2sin(B)

Therefore, the expression simplifies to 7/3 - 2sin(B), where cos B = -1/3.