The Economic Recovery Tax Act of 1981, which cut the top rate of tax from 70% to 50% (among other effects), and:
The Tax Reform Act of 1986, which cut the top rate of tax further from 50% to 28%, but primarily simplified the tax code.
I expect if you are being asked for one of these, it will be the first one - this was focused on cutting tax after the high rates during the 70s, while the second cut was more focused on simplifying the tax code. In either case, the 79% and 37% figures are a little off. Whether or not they were responsible for stimulating 2 decades of growth is a slightly more subjective question of course!