Assume the relationship is a direct variation, what is the equation?

please help me !!

Cora bought a package of erasers. there are 4 pink erasers and 12 blue erasers. what is the ratio of pink erasers to blue erasers?

What ratio is proportional to 18/21

Robert has 78 tomato lants and 56 cucumber plants .he wants to plant them in rows that only have one type of plant in each row with the same number of plants in each row. how many plants should he put in each row and how many rows of each type of plant will he need