5,4(-3 1/3)+13,8 = 5 (-10/3) + 13 + 8
= -50/3 + 21
= -50/3 + 63/3
= 13/3

1 13/15 + 3 5/6 = (1 + 3) + (13/15 + 5/6)
= 4 + (78/90 + 75/90)
= 4 + 153/90
= (360/90 + 153/90)
= 513/90
= 57/10

Therefore, the final answer is 57/10.