<em>The cabinet's center will be at the same place as the wall's center</em>. The wall's center is at its <em>3 1/8 ft mark</em>. The cabinet's center will also be at the wall's 3 1/8 mark. This means that both sides of the cabinet is <em>1 3/4 around the center line</em> (if my wording is vague, look at the image). So, we have to find <em>3 1/8 - 1 3/4</em>, which is 1 3/8 ft.