I have to integrate K(1-t)^4 dt between 0 and y

I get: K(1/5)(1-t)^5 the book has k(1-t)^5/(-5) i dont know how they got -5

then when i evaluate at 0 and y i get:
(k/5)[(1-y)^5 -1] and at this spot the book has (k/5)[1-(1-y)^5]

thanks