The table gives values of a differentiable function s at unequally spaced x-values.
x
0.0
0.7
1.5
2.6
4.0
s(x)
10.0
11.8
13.1
14.0
14.6
Using only the information in the table, determine whether s is concave up or concave down on the interval 0<x<4. Support your conclusion with a comparison of successive average rates of change.