Answer
$x=472cm$
Work Step by Step
$f=85cm$
$m=3.25$
$d_i=d_om$
$d_om=\frac{1}{\frac{1}{f}-\frac{1}{d_o}}$
$3.25d_o=\frac{1}{\frac{1}{85cm}-\frac{1}{d_o}}$
$3.25d_o=\frac{85d_o}{d_o-85}$
$3.25d_o-276.25=85$
$3.25d_o=361.25$
$d_o=111cm$
$d_i=361cm$
$x=d_i+d_o=111cm+361cm=472cm$
