A nature photographer is using a camera that has a lens with a focal length of $4\mathrm{.}70$ cm$.$ The photographer is taking pictures of ancient trees in a forest and wants the lens to be focused on a very old tree that is $17\mathrm{.}4$ m away. a$)$ How far must the lens be from the film in order for the resulting picture to be clearly focused? Answer in units of cm

b$)$ How much would the lens have to be moved to take a picture of another tree that is only $2\mathrm{.}24$ m away? Answer in units of cm