The marked price of a smart TV is ₹ 18,000. The rate of GST is 18%. The price paid by the customer for the smart TV is:

Given,

Marked price = ₹ 18,000

Rate of GST = 18%

GST = $\frac{18}{100} \times 18000$ = ₹ 3,240

Price paid by customer = Marked price + GST

= ₹ 18,000 + ₹ 3,240

= ₹ 21,240.

Hence, option 4 is the correct option.