A radio station has a promotion in which it announces that a local petrol station will sell petrol at $1.10 cents per litre beginning in 30 minutes. Jack hops in his car and drives to the station to fill up his half-empty tank. He pays only $22 for 20 litres instead of the going price of $26. Did Jack save $4.00? Is the radio station doing its listeners a favour by offering this promotion? Briefly explain.