Dear Mr. Armstrong, 

I received your letter of 30th March this morning returning the draft of the catalogue we propose to send to our customers and wish to say at once how very grateful I am for all the trouble you have taken to examine the draft and comment on it in such detail. Your suggestions will prove most helpful.

I realize the value of time to a busy person like you and this makes me all the more appreciative of the time you have so generously given me.

Yours sincerely,