1. 57%/43% are of course approximations. 56%/44% is certainly possible, and 54.5/45.5 is if both opponents are playing random hands(100% of cards dealt to them).
40% avg pot equity is also just an approximation.
2.its been a while so even moreso then usual there can be mistakes, so here's my work.
hero's stack on the turn =60920 therefore if hero folds the turn hero's stack remains 60920.
for calling to be better than folding Hero's avg. stack after calling must be greater than 60920.

the turn bet is 19344, leaving 41576 behind for the river.

using 43% for how often hero river's a low (always the nutlow)
and therefore 57% for how often he bricks the river and folds.

for calling to be greater than or equal folding:

.43*X + .57*41576 => 60920

where x is hero's chipstack when he calls and makes a low and show's down, and 41576 is hero's chipstack when he calls and bricks while 60920 is hero's stack when he folds the turn

x= 86562

and using 40% for hero's avg pot equty when he rivers a low.

for 40% of the pot to be => 86562, pot has to be 216405

so, when is the avg. pot 216405

60920*3 + 38808 = 221568 (pot when all 3 go to showdown)

19344 *3 + 41576 *2 +38808 = 179992 (pot when 1 other goes to showdown and 1 folds)

221568 *x + 179992 *(1-x) = 216405
41576x= =36413
x = ~87.6%