Two boys are standing on the opposite ends of a 540 metres long bridge. If they start walking towards each other at same time at the speed of 18 metres/minute and 12 metres/minute respectively, then in how much time will they meet each other?

The boys start from opposite ends of the bridge, so the distance that separates them initially is the full length of the bridge, $$540$$ metres.

When two objects move directly toward each other, their relative speed equals the sum of their individual speeds.
Speed of first boy = $$18$$ metres/minute.
Speed of second boy = $$12$$ metres/minute.

Therefore, relative speed $$v_{\text{rel}} = 18 + 12 = 30$$ metres/minute.

Time taken to meet is given by the basic relation
$$\text{Time} = \frac{\text{Distance}}{\text{Relative speed}}$$.

Substituting the values:
$$\text{Time} = \frac{540}{30} = 18$$ minutes.

Hence, they will meet after $$18$$ minutes.

Option A which is: 18 minutes