5. The value of k is the same of b in the original linear equation formula (y=mx+b). The b (or k here) changes where the equation itself fits on the graph. If a +0 is replaced with a -5, then the equation is shifted down by five units. I've graphed it below for you (where f(x) is in red and g(x) is in blue). Hope this helps!
in any y = mx + b formula, b is always the y intercept, and the y intercept is just a fancy name for where the line first crosses the y axis. hope this helps!