The shopkeeper purchases 5 cartoons for 105 rupees, which means the cost of one cartoon is:

Cost of 1 cartoon = 105 rupees / 5 cartoons = 21 rupees per cartoon

Similarly, the shopkeeper purchases 8 cartoons for 155 rupees, which means the cost of one cartoon is:

Cost of 1 cartoon = 155 rupees / 8 cartoons = 19.375 rupees per cartoon

We can find the total cost of 13 cartoons (5+8) as:

Total cost of 13 cartoons = 5 x 21 + 8 x 19.375 = 105 + 155 = 260 rupees

Since one cartoon contains 5 items, the total number of items purchased is:

Total number of items = 13 cartoons x 5 items per cartoon = 65 items

Therefore, the average price per item can be calculated as:

Average price per item = Total cost / Total number of items = 260 rupees / 65 items = 4 rupees per item

Hence, the average price per item is 4 rupees.