https://foxoyo.com/mcq/81030/a-can-contains-a-mixture-of-two-liquids-a-and-b-in-the-ratio-75when-9-litres-of-mixture-are-drawn-off-and-the-can-is-filled-with-b-the-ratio-of-a-and-b-becomes-79-how-many-litres-of-liquid-a-was-contained-by-the-can-initially