Answer:
Step-by-step explanation:
We notice that every time one the number increases, it increases by 3. To find it, first we subtract 4.5 and 3 to get 1.5 and this point is going to be (2, 1.5) Now, to find the cost of 1, we have to subtract 3 again to get (1, -1.5)
The cost of one pen is -1.5
