Explanation
Let the capacity of drum $$= x$$ liters.
Initially, the drum was $$\dfrac{3x}{4}$$ part filled. When $$15$$ liters oil is drawn then it becomes $$\dfrac{7x}{12}$$ part.
Now, according to the question,
$$\dfrac{3x}{4}$$$$-\dfrac{7x}{12}=15$$
$$\dfrac{9x - 7x}{12} = 15$$ { $$LCM(4,12)=12$$ }
$$2x = 180$$
so, $$x = 90$$ litres. Hence, B is right option.
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