Given a Horizontal Derivative Kernel What Would Be the Output Image?
The solution provided is correct. Here is why. 

To compute the derivative at index(3,5)

d(3,5) = value_at(4,5) - value_at(2,5)
d(3,5) = 150 - 0 
d(3,5) = 150


Hence the solution provided there is correct. Hope this helps :)