We are told Johanna already has 28 plants in the garden, but she needs to have 80 plants total. So first we must calculate how many more plants she needs to buy given what she already has.
Johanna needs to buy 52 more tomato plants. However, we are told that tomato plants are sold in packages. Each package contains 6 plants. To determine the number of packages Johanna must buy we need to divide the number of plants she needs by the number of plants in a package.
Therefore, Johanna will need to buy 9 packages of tomato plants in order to get enough.
Nine packages of plants contain 54 tomato plants. This is 2 more than the 52 she needs to reach 80, but it is the closest she can get given the plants are sold in packs of six.