3.(17%) Transform a third-order linear differential equation y"+2y"- y'-2y = 0 into a system of first-order simultaneous Jinear differential equations, and use only the matrix method to solve the problem.

6. (18%) Using the following relation, namely where A is the surface enclosing the volume △V, expand and explicitly write out ∇• B in spherical r-θ-Φ coordinates. Note that . Show all details to get full credit.