15y^2 + 30y = 15y (y + 2)
15y^2 + 30y = 3 * 5 * y * (y +2)
5y^2 + 35y + 50 = 5 (y^2 + 7y + 10)
5y^2 + 35y + 50 = 5 (y + 2) (y + 5)
the lcm is 3 * 5 * y * (y + 2) * (y + 5) because 3 * 5 * y * (y + 2) * (y + 5) contains 3 * 5 * y * (y + 2) (to make 15y^2 + 30y) and 5 (y + 2) (y + 5) (to make 5y^2 +35y + 50).
the lcm is 15y(y+2)(y+5)