In a plant nursery, the owner thinks that the lengths of the seedlings in a box sprayed with a new kind of fertilizer has an average height of 26cm after three days and a standard deviation of 10cm. One researcher randomly selected 80 such seedlings and calculated the mean height to be 20cm and the standard deviation was 10cm. Will you conduct a one-tailed test or two-tailed test Proceed with the test using α = 0.05.