If you were looking to make £100 profit, before commission, by laying the draw at 5.0 and then backing it at 7.0. You would need to lay at 5.0 to take £350 form the backer meaning you would need a liability of £1,400. If the draw then reached 7.0 and you wanted to back it you would need to do this for £250.
This would then leave you with a greenbook on the market for £100. (before commission)
In regards to you backing at 2.0, you would need to stake £1,400 in order to make £1,400 profit to cover the loss of the lay bet placed at 5.0 with the liability of £1,400. (This would be based before commission was taken into account as this would differ from customer to customer. You would need to take in to count how much commission will be take from the winning bets.)
When you are placing bets on the market you will see that the figures will appear in green and red to help show you your outcome on each option. You can also turn on in the settings for it to take into consideration the payout including commission.
I hope this has helped clear this up for you. If not one of agents on our customer service team would be more than happy to discuss this with you on the phone so and question you have can be answered at each stage.