In order to obtain a real image of magnification 2 using a converging lens of focal length 20 cm, where should an object be placed

Q. How far an object must be placed in front of a converging lens of focal length 10 cm in order to produce an erect image of linear magnification 4?

Q. At What distance from a converging lens of focal length $12cm$ must an object be placed in order that an image of magnification $1$ will be produced?

Q. Where should an object be placed from a converging lens of focal length $15cm$, so as to obtain, a real image of same size as that of the object?

Q. A diverging lens of focal length 20 cm and a converging mirror of focal length 10 cm are placed coaxially at a separation of 5 cm. Where should an object be placed so that a real image is formed at the object itself?

Q. A diverting lens of focal length $20cm$ and converging mirror of focal length $10cm$ are placed coaxially at a separation of $5cm$. Where should an object be placed so that a real image is found at the object itself?