Answer
$2.95m$
Work Step by Step
As we know that
$d_i=\frac{h_i}{h_{\circ}}d_{\circ}$
We also know that
$\frac{1}{f}=\frac{1}{d_i}+\frac{1}{d_{\circ}}=\frac{h_{\circ}}{h_i d_{\circ}}+\frac{1}{d_{\circ}}=\frac{1}{d_{\circ}}(1-\frac{h_{\circ}}{h_i})$
This can be rearranged as
$d_{\circ}=f(1-\frac{h_{\circ}}{h_i})$
We plug in the known values to obtain:
$d_{\circ}=0.055(1-\frac{1.9}{-0.036})=2.95m$