"수자를 나타내는 한자들은 간단하여 익히기가 귑다" => 숫자를 나타내는 한자들은 간단하여 익히기가 쉽다 (귑다 -> 쉽다). => Hanja characters representing numbers are simple and easy to learn. (Hanja characters representing numbers are so simple they're easy to learn) "여" in 간단하여 is connective ending -아/어 for the verb 간단하다 (it's an irregular case: 하 + 아/어 => 하여/해). -아/어 connects a verb to the next verb or phrase, expressing successive actions or cause and effect relation. * 저녁엔 불고기를 해(서) 먹자: Let's make (and eat) 불고기 for dinner. (successive actions: 하(다) + -아/어 + 먹자) * 집이 넓어(서) 편하다: The house is big, which makes it comfortable. (cause and effect). (Attaching 서 adds clarity and emphasis to the first verb) -아/어 is also important because it makes many common verb phrases. Here are some examples: * 먹어 보다, 해 놓다, 놓아 두다, 찾아 주다, 되어 가다, 밝아 오다, 끝내 버리다, 맑아지다.

That's a commonly used style in formal texts. Roughly: 간단하여 = 간단해서 하다 is actually conjugated 하여, with 해 being its abreviation. Just like 주다 and 보다 are conjugated 주어 and 보아, but everyone mostly uses the abreviations 줘 and 봐. As for why -어서 is omitted... Well I don't exactly know. I guess they omit it because it's a common pattern and the meaning is already clear. Like: -이라서 → -이라 위해서 → 위해 (위하여) 대해서 → 대해 (대하여) 향해서 → 향해 (향하여)