Please help with the following Physics questions

Two thin lenses are convex with a focal length of magnitude:10.0cm and the other concave with a focal length of magnitude 15.0 cm, are combined as shown in Fig. 3.1. O 15.0 cm Fig.3.1 (a) Find the focal length of the lens combination. (b ) Calculate the position of the image of the object O placed 15 cm from the combination lens. (c) Determine the magnification of the object. (d) Draw a ray diagram to show how the image is formed. [10]