Why does the graph of a function shift left when K is positive and to the right when K is negative?

You can visualize this easily.

y=f(x+h)

Now if the argument of the function is taken as (x−h) the value of y will be f((x−h)+h)=f(x)  

The function y acquires the value of f(x) at (x−h) amounting to a left shift.

Hope this makes things clear.

Step-by-step explanation:

they used 313 gallons of paint