Which of the following is the integrating factor for (3xy+y2)+(x2+xy)y′=0(3xy + y^2) + (x^2 + xy) y' = 0(3xy+y2)+(x2+xy)y′=0?
μ=x\mu = xμ=x
μ=y\mu = yμ=y
μ=xy\mu = xyμ=xy
μ=x+y\mu = x+yμ=x+y