https://buymiles.mileageplus.com/united/index_en.html Buy 5,000 - 19,000 miles | Get a 25% bonus Buy 20,000 - 39,000 miles | Get a 50% bonus Buy 40,000 - 75,000 miles | Get a 100% bonus ですので、例えば 40,000マイルを購入すると、ボーナス 4…