f(1)+f(2)+1=f(4)≤6 f(1)+f(2)≤5 Case (i) f(1)=1⇒f(2)=1,2,3,4⇒4 mappings Case (ii) f(1)=2⇒f(2)=1,2,3⇒3 mappings Case (iii) f(1)=3⇒f(2)=1,2⇒2 mappings Case (iv) f(1)4⇒f(2)=1⇒1 mapping f(5)&f(6) both have 6 mappings each Number of functions =(4+3+2+1)×6×6=360