Find an outie from a Killer box

A Sudoku box also contains one through nine, so it totals forty-five. Here, three Killer cages cover the whole box. But look closely: the bottom cage crosses the box edge. It takes one extra cell with it. That outside cell is called an outie. Add the three cage clues: six, fifteen and twenty-five. They make forty-six. That counts every box cell once, plus the outie once. The box itself totals forty-five. The cages total forty-six because of the one cell that sticks out. So that cell must be one. When cages cover a box and spill over by one cell, subtract forty-five. The difference is your outie.