Using the RSA public key cryptosystem, and assuming the two prime numbers $($p and q$)$ are

p $=3,$ q $=11.$

a$)$ If d $=7,$ find e$.$

b$)$ Assume the English alphabet is represented as the sequence of decimal numbers, i$.$e$.,$ a$=1,$ b$=2,$ c$=3,$ d$=4,$ e$=5,..$

$.....$y$=25,$ z$=26$

Encrypt the word "hello", then decrypt it$.$