プログレッシブ和英中辞典(第4版)の解説
こうじん【幸甚】
茶会にご出席いただければ幸甚に存じます
It would give us great pleasure if you could attend [be at] the tea party.
折り返しお返事くだされば幸甚に存じます
If you could send us a reply by return mail, we would [should] be much obliged.／We would [should] greatly appreciate an immediate reply to this letter.