Question

Could someone explain how to find the answer to this? I forgot how -_-
The variation of kernel color in corn plants is an inherited trait. R is the dominant allele for red kernels in a corn plant and r is the recessive allele for yellow kernels.

What is the probability that a corn plant with the genotype Rr crossed with a corn plant rr will have offspring with the genotype rr? Express your answer as a fraction using numerals for numbers and / for the fraction bar.