Well, the category is cryptography, and Gamer says the fact that the "3=R" line appears twice is unintentional (a coincidence). There are 3 symbols in "3=R" and the most common three letter word is "the" which would give us 3 => T, = => H, R => E
But, is it reasonable to assume that all the words end in the format -Hx or -Hxx, especially if we'd be looking for four different "x"es, none of them "E"
(re: Hints)
