$\frac{6}{7}$ th part of a tank is filled with oil. After taking out 60 litres of oil, the tank is $\frac{4}{5}$ th part full. What is the capacity (in litres) of the tank?

Let the capacity of the tank be x litres. According to the question,

$\frac{6 x}{7}-\frac{4 x}{5}=60$

$\Rightarrow \frac{30 x-28 x}{35}=60$

$\Rightarrow \frac{2 x}{35}=60$

$\Rightarrow 2 x=60 \times 35$

$\Rightarrow x=\frac{60 \times 35}{2}=1050$ litres