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Please see the official X‑Plane Support page for help.
The system you described is adequate to run X-Plane 11. With rendering settings at medium to medium-high, it should achieve 25+ FPS. There are other factors you have not specified: display resolution, type of aircraft etc. Flying X-Plane’s generic airplanes at single 1080p—no problem. But with some of the complex payware aircraft and/or at higher resolutions, FPS may get a bit edgy.
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