A 3.6 GPA is a solid A- and puts you in the top 25% of US high schoolers. It's the practical floor for serious application to mid-tier private universities (Boston University, Northeastern, Tulane, USC) and for direct-admit consideration at competitive state flagship business and engineering programs. The number also clears the bar for most professional honor societies and competitive merit scholarships requiring 3.5+.
A 3.6 unweighted GPA is the median admit number at many top public universities' business schools (Indiana Kelley direct admit, Texas A&M Mays). With 3.6 + 1300+ SAT, you're in the typical admit profile at most US News-ranked top-100 universities.