For 100 km, a taxi charges ₹ 1 ,800. How much will it charge for a journey of 120 km ?

Let the taxi charges ₹ x for 120 km.

Since it is a case of direct variation,

$\therefore \dfrac{100}{1,800} = \dfrac{120}{x}\\[1em] \Rightarrow x = \dfrac{120 \times 1800}{100}\\[1em] \Rightarrow x = \dfrac{2,16,000}{100}\\[1em] \Rightarrow x = 2,160$

Hence, the taxi will charge ₹ 2,160.