Rates unite rates and ratios

50 candles in 4 boxes

Unit rate is the quantity per one. In this case it is how many candles per 1 box.
You divide everything by 4 to get 12.5 candles per 1 box (or 12 candles in 4 boxes and 2 left over.)

The ratio between candles in boxes would just be 50 candles to 4 boxes, or 50:4. You can simplify it to the unit rate of 12.5 candles to 1 boxes, or 12.5:1

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The first option would be correct if it were one half and not one