In the given interval 1 < x < 6, the function is decreasing.
As seen from the graph, the value of function is lower at every next value of x than its previous value. For example value function is lower at x = 2 as compared to x = 1. Likewise the value is lower at x = 3 than x = 1 and x = 2 and this continues till x= 6. Therefore, the function is decreasing.
Another way to look at the problem is see the slope of the function. The line is constantly falling down, which means it is a decreasing function.