Physics Help regarding Optics?

Question

A slide projector has a converging lens whose focal length is 105 mm.

(a) How far (IN METERS) from the lens must the screen be located if a slide is place 108 mm from the lens.?

(b) If the slide measures 24.0 mm x 36.0 mm , what are the dimensions ( in mm) of its image?

Can someone please help me I've tried so hard to get an answer

Answer 1

the law is:

1/a + 1/b = 1/f

a=108 mm

b=?=distance of screen

f=105 mm

b=3.780m

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enlargement is:

image = slide * b/a