A linear fuction is one in which the relation between the dependent variable (number of objects in this case) and the independent variable (ship number in this case) is a constant plus a factor times the independent variable.
This is is y is the number of objects and x is the ship number:
y = A + Bx, where A and B are constants.
So, you must find a function with that form, where A is the number of objects when the ship number is 0, and B is the amount that the number of objects increase divided by the amount that the ship number increase, taking any two points.
