Thankyouforyourletterof[date].
Imgladthatyouarealsogoingto[place]nextmonth.itwouldbeagreatpleasuretomeetyouatthe[exhibition/tradefair].ourcompanyishavingareceptionat[hotel]ontheeveningof[date]andiwouldbeverypleasedifyoucouldattend.
Ilookforwardtohearingfromyousoon.
Yourssincerely,[name][title]