## Fundamentals of Physics Extended (10th Edition)

The image distance is given by $i = -mp$ By substituting m = -0.40 and p = +30 cm, we find: $i=-(-.4)(30)= +12 cm$ By substituting i = +12 cm and p = +30 cm into the equation, we obtain: $1/f = 1/p + 1/i\\\\ 1/f = 1/30 + 1/12\\\\ f = +8.6 cm$