A homeowner looked at her electric bill over the past six months and noticed that the bill has been increasing as is shown in th

B. quadratic. To determine whether a function is linear, quadratic, or exponential without graphing, examine the first, second, and third differences between the terms. If the first differences remain constant, the function is linear; if the second differences are constant, it is quadratic; if the third differences are constant, it is cubic. If the fourth differences do not remain constant, the function may be exponential. Here, the first differences are not constant, ruling out linearity. However, the second differences are constant (around $0.18 each), indicating a quadratic function. The accompanying graph supports that the points closely align with a quadratic model.