Underlined step is not clear to me please explain it .....how that pie came there ?????is there any mistake?

19. A gas of non-relativistic classical particles in 1-d is subjected to a potential V(x) = alx), where a 1 is a constant, the partition function is B= (NET June 2016) KT 4Ttm 8m (B) (A) h'a p S 27tm |37tm ha'p (C) (D) hfaB p