Usage of よって in this sentence

Question

I am currently doing some exercises for my Japanese class, but they are all in hiragana, which is sometimes irritating, but in this sentence I fail to see the meaning　and thus unable to pick the suitable answer, 3:

ゆうびんきょくに　＿＿　かえります。

Available answers are :

1) やんで　2) よんで　3) よって 4) やって

I thought ~による was used in a sense similar to "According to..." but I really don't see how this fits within the sentence.

Is this another usage of the above form ?

A different verb ? I really think it is more of a suite of actions, "Do something at the post office and come back". I really wish I had a kanji there to help me out... As a bonus, why do textbooks often contain no kanjis and only hiragana ? This seems more confusing that anything else to me.

Thanks !

Answer 1

I think this よって comes from the verb 寄る{よる} which means "to visit, to drop by" in this case. Your sentence thus means:

ゆうびんきょくによってかえります。
I'll drop by the post office and come back.

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～によると is used as "according to" (see よると or よれば？ Which one is "according to"?).

～によって can mean "by way/method", "depending on", "because of" (see What´s the difference between による, により and　によって?).

Neither of them can be applied to "post office" in this sentence though.