Roast beef with a rich brown gravy is often described as a "savory" dish. the basic taste prominent in such a dish is:

The answer is "umami".

Umami refers to the savory taste which is one of the five essential tastes (together with sweetness, harshness, intensity, and saltiness). It has been depicted as appetizing, and normal for juices and cooked meats. Individuals taste umami through taste receptors that normally react to glutamate. 

g(x) = 2f(x) > y-intercept at (0,2)

h(x) = f(x)+2 > asymptote of y=2

j(x) = f(x+2) > y-intercept at (0,4)

m(x) = function decreases as x increases