The question is wrong actually there should be page size=2MB but they have given page table size as 2MB.
If they have given page size as 2MB, answer as follows..
when we use paging, the last page may not be used by the process completely, on an average last page will be half full.
P has three sections namely text, heap and stack and if the size of the page is 2 MB. so for every section it may waste half page.
total wastage=3*1MB=3MB