Series (recurrence formula) question - find p

Hello,

I have worked out two terms in a series, the question is as follows

A sequence of terms is generated using Uk+2 = Uk+1 - pUk
U1 = 2 and U2 = 4

U3 = 4-2p
U4 = 4-6p

Part c asks 'Given U4 is twice the value of U3, find the value of p'

Basically I'm not sure how to work out to get p given the fourth term is twice the value of the third. Can anyone point it out?

Thanks

Got it, thank you and others for being on hand, it's very helpful and appreciated.