Hot dog cost = 3.50x2 = $7
 Peanuts cost = $4
 A Coupon of $3 
 Total paid amount by mark = $11.50
 Cost of a large soda = ?
 Total spent amount along with the coupon = 11.50 + 3 = $14.50
 The cost of hot dogs and peanuts = 7 + 4 = $11
 Thus the cost of large soda = 14.50 – 11 = $3.50