Hints
If we were told that f'(7.5) = -2.5 (for example), then we would know that the slope of the graph of function f is negative 2.5, at the location on the curve where the x-coordinate is 7.5.
This tells us that the graph of function f is going "downhill", in the vicinity of x=7.5.
It's not given, but I assume that function f is well-behaved (i.e., its graph is smooth and continuous).
What do the two given derivatives tell you about the behavior at x=6 and x=8?