Concept:Rank from the bottom is calculated using the total number of students and the rank from the top.Explanation:Total number of students in the class is 31.Anu is ranked 7th from the top.Anu's rank from the bottom is 31−7+1=25.So Anu is 25th from the bottom.Vinay is ranked 11th from the top.Vinay's rank from the bottom is 31−11+1=21.So Vinay is 21st from the bottom.Hence, their respective ranks from the bottom are 25th and 21st.Answer:Option C: 25th and 21st