Given, Amy, Bella, Serra, Diya, Emma and Phila are 6 students in a class. We have to arrange them in order of their height as well as their weight.
From the given information, Emma and Diya are shorter than Amy but heavier than Phila. We conclude the following:
Case 1: Amy > Emma, also Amy > Diya
Case 2: Emma > Phila also, Diya > Phila.
Here, Case 1 is used for height and Case 2 is used for weight.
Sera is heavier than Emma and taller than Diya.
Case 1: Sera > Diya
Case 2: Sera > Emma
Bella is shorter than Sera but taller than Amy.
Case 1: Sera > Bella > Amy
Amy is heavier than Sera.
Case 2: Amy > Sera
phila is shorter than Bella but taller than Amy.
Case 1: Bella > Phila > Amy
Now, on combining all Case 1 and Case 2 from the above statements we conclude:
Case 1: Sera > Bella > Phila > Amy > Emma/Diya
Case 2: Amy > Sera > Emma/Diya > Phila
No information was given about the weight of Bella so Case 2 can't be formed properly, only case 1 is shown completely with the given information.
Descending order of their length:
Sera > Bella > phila > Amy > Emma/Diya
Hence, Amy will be in fourth place from the top if they are placed in descending order of their length.