When mendel crossed peas with rr and rr genotypes (where r is dominant and produces wrinkled peas and r is recessive and results in smooth peas) the phenotypic percentage of the offspring being wrinkled was?

I think your question all turn into lowercases, uppercases, and lowercases are important in genetics because it can differentiate between the dominant and recessive forms. 
let me explain at least how to calculate the offspring percentage:
for example, you have Rr crossed with another Rr (R for wrinkled peas and r for smooth peas), you just have to match between the four letters, and you will have four possibilities:
R and R
R and r
r and R
r and r
you will have RR, Rr, Rr, and rr
if we convert into percentages, it will give: 
25% RR
50% Rr (there's two Rr so 25 + 25)
25% rr