To be honest, I'm not sure what this question is supposed to be solving.

The only possible answer I can think of is the following:

The only numbers that are equal for x/4 and y/5 are multiples of 4 equal x and multiples of 5 equal y (0 included.) What that has to do with the problem might need more explanation, perhaps I don't understand the context of the problem.

BUT for x+1 = z/5

z = 5x+5 for all real numbers.

x+1 = z/5
(multiply both sides by 5)
5x+5 = z

Is there any more explanation on your assignment?