An object is placed 20cm in front of a concave mirror of focal length 15cm. The mirror is then replaced at the same position by a convex lens of the same focal length. Which option states the nature of the images formed by the mirror and the lens respectively?
a) Mirror: real, inverted; Lens: virtual, erect
b) Mirror: virtual, erect; Lens: real, inverted
c) Mirror: real, inverted; Lens: real, inverted
d) Mirror: real, erect; Lens: real, erect