Awebsite uses the formula above to calculate a seller’s rating, r, based on the number of favorable reviews, f, and unfavorable reviews, n. which of the following expresses the number of favorable reviews in terms of the other variables? f=rn/r-1 f=rn/1-r f=n/1−r f=n/r−1

The correct formula is

RN/(1-R) = F.

To solve for F, we start by multiplying by (N+F) to remove it from the denominator:
R(N+F) = F

Distributing, we have:
RN + RF = F

Subtracting RF to collect all of the F's on one side,
RN = F - RF

Factoring out F on the right hand side,
RN = F(1 - R)

Dividing both sides by (1-R), 
RN/(1-R) = F