Initiative: 13 + 15/2 = 21

Trey's hit roll: 5 + 15/2 = 13
Enemy's dodge roll: 3 + 4/2 = 5
Trey's damage rolls: 1 + 4 + 17/2 - 1 = 13
Trey's remaining MP: 0/10
Enemy's remaining HP: 7