Correct Answer - Option 3 : 4√3 cm

**Given:**

Area of equilateral ΔPQR = 36√3 cm^{2}

**Concepts used:**

Area of equilateral triangle = (√3/4) × (Side)^{2}

Circumradius (R) of equilateral triangle = Side/√3

**Calculation:**

Area of equilateral triangle = (√3/4) × (Side)^{2}

⇒ 36√3 cm^{2 }= (√3/4) × (Side)^{2}

⇒ (Side)^{2 }= 36 × 4 cm^{2 }

⇒ Side = √144 cm

⇒ Side = 12 cm

Circumradius (R) of equilateral triangle = Side/√3

R = 12/√3 cm

⇒ R = 4√3 cm

**∴ Length of circumradius is equal to 4√3 cm.**