Answer:
The function is 
She would be charged $69 dollars for 22 items.
Step-by-step explanation:
We are given that,
Jane was charged $15 for buying 4 items.
Jane was charged $39 for buying 12 items.
Since, we have,
15 = 3 × 4 + 3
39 = 3 × 12 + 3
So, the function modeled for this situation will be,
Let, y = amount of money charged in dollars and x = number of items bought.
Then, the function is
.
Further, when she purchases 22 items, the cost would be,
implies
i.e. y= 69 (dollars)
Hence, she would be charged $69 dollars for 22 items.