An eraser of height 1.0cm is placed in front of a two-lens system. Lens 1(nearer the eraser) has focal length f1=-15cm, lens 2 has f2=12cm, and the lens seperation is d=12cm. For the image produced by lens 2, what is the image distance i2? What I did is setup some equations. For lens 1: 1/-15 = 1/P1 + 1/i1 and m1 = -i1/P1 For lens 2: 1/12 = 1/(i1+12) + 1/i2 and m2= -i2/(i1+12) I'm having trouble solving this. I can't get past having one more unknown than equation. Any help will be appretiated, thanks.