Because 0.75 is less than 1, the bigger x is, the smaller the whole thing will get. And the 4.1 in front is the starting point on the left side of the graph. Like on an actual graph with numbers:
If x is 0, f(x) is 4.1
If x is 5, f(x) is 0.97
The graph is decreasing. This is an equation and graph for "decay"