When did Spencer Silver discover the formula for the "unglue"?

several years before Fry had his idea

the year before Fry had his idea

at the same time Fry had his idea

soon after Fry had his idea

Several years before Fry had his idea.

Explanation:

The Evolution of Useful Things by Henry Petroski deals with the issues of small trivial things and how they came to be. These small details may seem trivial but in actuality, they play a huge part in our lives. Petroski delves into the details of these things and how they have a huge impact on our lives.

Spencer Silver was a 3M researcher who had come upon the formula for the "unglue" while working "in the course of developing very strong and very tacky adhesives". This was several years earlier, before Art Fry, a chemical engineer who came upon the idea in 1974.