Split the alleles for each parental type and add them into your Punnett square around the edges ... The probability values must add up to 100% (25 + 50 + 25 = 100). The ratio can be summarised ...

Determine the probability that the offspring will have grey fur. In this Punnett square the top row shows the alleles of parent 1 and the left-hand column shows the alleles of parent 2.