The independent variable is the variable whose variation does not depend on another external variable. It is the variable on the x-axis which in this case is the growth of the baby.
Note: The diagram you attached to this question does not include the calibration on the x - axis which will give us the independent variable at point
This, nevertheless, is a very simple task. Locate the point A on the graph and trace it downwards to the x - axis, the value written where the line coincides with the x -axis is the value of the independent variable( growth of the baby) at point A.
Divide the amount she drove by the total amount she needs to drive, them multiply that answer by 100 to make it a percent. This will give you the percentage she drove. To find the percentage she has left,, subtract from 100%.