Why is d/dx (4) = 0 in derivative

Shouldn't it be 4/x?

Derivative gives a slope of a line
4 is a constant number.
You can not draw a line to the number 4.
Hence no slope, that is, its derivative is zero.

Derivative of a constant is always Zero. Because derivative always de-grades a value while on the other hand Integration always up-grades a value.

You should write it as d(4) / dx instead of d / dx (4).

Proof:-
f'(x) = Lim(h-->0) [ f(x + h ) - f(x) / h]
= Lim(h-->0) [ c - c / h] where ''c'' represents a constant
= Lim(h-->0) [ 0 / h]
= Lim(h-->0) [ 0 ]
= 0

Please see here d/dx means rate of change of 4 as 4 is a fixed value so there is not change in it hence it' rate of change is zero

or we can see in in other way we we plot the graph for y=4 we got a line parallel to x axis and d/dx gives slope of it
as y=4 has slope of zero hence d/dx(4)=0

the derivative of a constant is always 0

No, d/dx has Special Meaning, not like general Algebra.