These are Colorano Silk Maximum Cards with the three pairs of 15-cent letter writing stamps. These stamps were issued on February 25, 1980 in Washington, DC. Jimmy Carter was president at the time, and that looks like him on the silk cachet of the last card. This set of postage stamps were issued during National Letter Writing Week and focused on the importance of letter writing, The themes name three benefits of letter writing: preserving memories, lifting spirits, and shaping opinions.
The picture below gives a better idea of what they looked like when issued. (Source: Postal Service Guide to U.S. Stamps).
This is a post for Sunday Stamps at Viridian's Postcard Blog