Answer :
You would need to subtract the 26 dollars by the 5 dollar shake to get 21 which is the amount he spent on all the shakes. Now divide 21 by 6 and your answer would be $3.5 per Sunday
($3.5 x 6 (amount of shakes) = $21 which is the amount he had after buying the $5 supersize shake)
($3.5 x 6 (amount of shakes) = $21 which is the amount he had after buying the $5 supersize shake)