ANSWER
The cost of apples is a function of their weight.
Step-by-step explanation
On the cartesian plane, the horizontal axis is the x-axis and the vertical axis is the y-axis.
The values on the y-axis are the values of the dependent variable while the values on the x-axis are the values of the independent variable.
This implies that, generally, for a function, y is a function of x.
Therefore, the cost of apples is a function of their weight.