What percentof the offspring will be HOMOZYGOUS if a HETEROZYGOUS ROUND seed plants crossed with a homozygous?

1/2 Will be homozygous dominant (RR)
1/2 Will be heterozygous (Rr)

50% i f you do the punnet square two are RR and the other two are Rr

_________R______R                     x (Homozygous)
                                               y (Heterozygous
__R_____RR_____RR

__r______Rr______Rr
     

See the table? RR crossed with Rr would produce 2 homozygous and 2 heterozygous offspring, (50% RR and 50%Rr). Remember however that This is speaking strictly of the genotype. An RR has a homozygous genotype and will thus have a homozygous phenotype however the heterozygous offspring, (The Rr), will have a heterozygous genotype yet it will also show a homozygous phenotype because as I'm sure you know, R is dominant over r. Got it?
  For further help I highly recommend the Khan Academy, (best site on earth in my opinion), (Khanacademy.org) as well as another site that calculates Punnett squares for you, ChangeBioScience.org. The links are below.
Enjoy!

http://www.khanacademy.org/video/punnett-square-fun?playlist=Biology
http://www.changbioscience.com/genetics/punnett.html