Hedging a Treble

I placed a bet at the start of the season on three teams to get promoted. One leg of the bet has already come in, the other two are west ham (1.75 to lay) and huddersfield (4.1 to lay).

The stake was £20 and stand to return £200 profit if all selections win.

Could anyone tell me how to calculate how much I would need to lay both west ham and huddersfield for in order to return an equal profit incase either of these teams do not get promoted?

Thanks for your help.