Let x be the price of each of the 8 bags from the first shop. Find the following (use x if necessary).

(1) Price of 8 bags from the first shop

(2) Average price of bag from the first shop

(3) Total price of bags from the second shop

(4) Total price of bags from both shops

(5) Total price of bags from both shops

(6) Average price of bags from both shops

Then the equation is: the answer for (2) - the answer for (6) = 1.50