Encrypt the message " HALT " by translating the letters into numbers
(via $A=0,B=1,C=2,D=3,E=4,F=5,G=6,H=7,I=8,$
$J=9,K=10,L=11,M=12,N=13,O=14,P=15,Q=16,R=17,$
$S=18,T=19,U=20,V=21,W=22,X=23,Y=24,Z=25$ )
and then applying the encryption function given, and then translating the numbers back into letters.

(a) $f(p) = (p+2) \text{ mod } 26$

(b) $f(p) = (p+11) \text{ mod } 26$

(c) $f(p) = (p+3) \text{ mod } 26$