What is this correct answer?

Two customers went to a post office. first customer paid $12 for 14 and 5 envelopes the second paid 24.80 for 10 postcards and 15 envelopes. what is cost of each envelope?

What is the value for this expression? 2e-5

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