The w in answer is silent today, but it was not always just an extra letter. The word comes from older forms of English, including Old English andswaru. In earlier stages, the spelling reflected sounds and related word forms more closely than modern pronunciation does.
As English changed over time, some consonant sounds became weaker or disappeared in everyday speech. Spelling, however, often changed more slowly. That is why modern English still writes answer with a w, even though most speakers do not pronounce it.
This is not unusual in English. Many words preserve older spellings after pronunciation has shifted.
- sword: the w is written, but usually not spoken
- two: the w remains from an older pronunciation history
- write: the w stayed after the sound became silent
So the silent w in answer is basically a historical clue. It shows that English spelling often keeps a record of the past, even when modern speech has moved on.