To find the rate of change in Ai Mi's savings, we look at the change in savings over the change in weeks. The rate of change can be calculated using any two points from the table.

Let's use the points (4, $56) and (7, $71):

Rate of change = $\frac{{\text{Change in total savings}}}{{\text{Change in weeks}}}$

Rate of change = $\frac{{71 - 56}}{{7 - 4}} = \frac{15}{3} = 5$

So, the rate of change is $5 per week.