9.20 let s be the surface of the cone z = +bounded by the planes z =o and z = 3. further, let c be the closed curve forming the boundary of the surface s. a vec

9.20 Let S be the surface of the cone z = +bounded by the planes z =O and z = 3. Further, let C be the closed curve forming the boundary of the surface S. A vector field F is such that x F=-xl-y). The absolute value of the line integral F-df, where i=xi+y]+ zk and r = lPl is (A)0 (B) 9 (C) 15 (D) 18