Either A) 10% or B) 4% would work.
Technically, the margin of error of a poll, in this case +/- 4%, would mean the actual populace might be either 4 points higher or 4 points lower than the reported 7% lead. So it could be as low as a 3% lead or as high as an 11% lead. So that's an 8 point range within which the actual voters might fall.
Notably, a study reported in the New York Times in 2016 found that most political polls actually have ended up with about a 6 to 7% margin of error compared to actual voting results. (That's a range of 12 to 14 points total between the minus end and the plus end.) So you can't always assume that polling results will predict actual election results.