Boston Mayor Michelle Wu called on her top challenger Josh Kraft to release his tax returns to reveal any financial interests or business “entanglements” he may have with the city that could impede his ability to effectively serve as its mayor.

The poll of 500 Boston voters likely to participate in the Sept. 9 preliminary election showed a wide gulf between Wu and Kraft, who drew 30 percent support to her 60 percent.

With weeks to go before the Sept. 9 preliminary election, the math remains daunting for Boston mayoral hopeful Josh Kraft.