What do these signs mean ² ³ √ ∛ · ≈ ≠ , ≡ ≅ ⇒ ⇔ ∈ ∉ ∧ ∨ ∞ α β Δ π Ф ω ↑ ↓ ∵ ∴ ↔ → ← ⇵ ⇅ ⇄ ⇆ ∫ ∑ ⊂ ⊃ ⊆ ⊇ ⊄ ⊅ ∀ ∝ ∦ ║ ⊕ ¬ ∅ ∩ ∪ ⊥ ∡ ∠ ° ∞ ㏒ ㏑

if you can answer this i will name you the brainiest

The line plot below represents the number of letters written to overseas pen pals by the students at the waverly middle school. each x represents 10 students. how many students wrote more than 6 and fewer than 20 letters. a.250 b.240 c.230 d.220