Correct my answers if any, with explaintion

b) Using the encrypting function f(p)=(p+10)mod26,0p25, encrypt the message "DEAR DOCTOR". Q-3: The relation R={(a,b)a+b=101} on the set of integers is a) Reflexive b) Transitive c) Symmetric d) Antisymmetric e) None of the above Q-5: The number of vertices in the complete bipartite graph K4,5 is a) 4 b) 5 c) 9 d) 20 e) None of the above Q-3: If a7mod13, then a may equal a) 0 b) 14 c) 19 d) 19 e) None of the above