(-x)7=-x7; (-x)4=x4, so (-x)7/(-x)4=-x7/x4=-x3.
Or you could solve it this way:
(-x)7/(-x)4=(-x)3=-x3.
The reason for this is that -x=(-1)×x, so (-x)n=(-1)n×(xn).
(-1)n=(-1)×(-1)×(-1)×... is either 1 or -1 depending on whether n is even or odd, because minus times minus is plus, so the product of two negative numbers is positive. So we can take negative numbers in pairs, knowing that their product is always positive. An odd number consists of a set of pairs with one over, and it's the sign of this odd one out that determines the final sign of the product.