Answer
$87mm$
Work Step by Step
We know that
$\frac{1}{f}=d_{\circ}(1-\frac{h_{\circ}}{h_i})^{-1}$
$\implies f=d_{\circ}(1-\frac{h_{\circ}}{h_i})$
We plug in the known values to obtain:
$f=3.0(1-\frac{1.2}{-0.036})=87mm$
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