Evaluate the surface integral ∫∫ s f · ds for the given vector field f and the oriented surface s. in other words, find the flux of f across s. for closed surfaces, use the positive (outward) orientation. f(x, y, z) = x i − z j + y k s is the part of the sphere x^2 + y^2 + z^2 = 25 in the first octant, with orientation toward the origin.