Correct Answer - Option 3 : 20 months

**Given:**

Principal, P = Rs. 3600

Rate, R = 15%

Amount, A = Rs. 4500

**Formula used:**

Simple interest = (P × R × T)/100

Simple Interest = Amount – Principal

**Calculation:**

Simple Interest = Amount – Principal

⇒ S.I = 4500 – 3600 = 900

Simple interest = (P × R × T)/100

⇒ 900 = (3600 × 15 × T)/100

⇒ 900 = 540T

⇒ T = 900/540

⇒ T = (5/3) × 12 months

⇒ T = 20 months

**∴ The required time is 20 months.**