import Mathlib

set_option maxHeartbeats 0

open BigOperators Real Nat Topology Rat

theorem mathd_algebra_215
  (S : Finset ℝ)
  (h₀ : ∀ (x : ℝ), x ∈ S ↔ (x + 3)^2 = 121) :
  ∑ k ∈ S, k = -6 := by sorry