Encrypt the message " MATH " by translating the letters into numbers
and then applying the encryption function given, and then translating the numbers back into letters.

(a) $f(p) = (15 p+2) \text{ mod } 26$

(b) $f(p) = (21 p+11) \text{ mod } 26$

(c) $f(p) = (19 p+3) \text{ mod } 26$

Use $A=0$,$B=1$,$C=2$,$D=3$,$E=4$,$F=5$,$G=6$,$H=7$,$I=8$, $J=9$,$K=10$,$L=11$,$M=12$,$N=13$,$O=14$,$P=15$,$Q=16$,$R=17$, $S=18$,$T=19$,$U=20$,$V=21$,$W=22$,$X=23$,$Y=24$,$Z=25$