The dependent variable according to the graph is the mass (along the y axis) while the independent variable is the time in days
This means that mass depends on the time in days.
The coordinate of the point A on the graph is (6, 3)
This means that at point A, the mass of the baby mouse is 3grams after 6 days.
Since the independent variable is along the x axis, hence the independent variable at point A on the graph is 6days