EV=f*$20+(1-f)*(0.4418*$110-0.5582*$90)

Solving for EV=0 to find the breakeven point: f=0.07578 or 7.58%

So he only has to fold 7.58% of the time to make the shove +EV. This makes sense because our equity against his calling range is pretty good (44+%), so he doesn't have to fold very much at all for the shove to be +EV.