Age of Grinnell Bros. upright

Answer 1

Your Grinnell Bros piano ser#400724 is most likely a 1971 Cable-Nelson (if it is the 40"- 42" console), manufactured by Everett in South Haven, Michgan (I have a 1972).  They were known as a low-cost decent quality piano.  Depending on the condition, they can go for about $800-$1000.

Answer 2

I'd like to know the Age of My Grinnell Bros piano ...  since it's serial number is 7637