Heterozygous male guinea pigs with black, rough hair (BbRr) are crossed with heterozygous female guinea pigs with black, rough hair (BbRr). The incomplete Punnett square below shows the expected results form the cross

Remember for a di hybrid cross with two completely heterozygous parents, the phenotypic ratio will always be 9:3:3:1

9 will always display both dominant traits, black and rough hair. 3 will display black hair and smooth hair and 3 will display not black hair and rough hair and 1 will display both receive traits