Correct Answer - Option 1 : 35 km

**Given that:**

Speed of first bike A= 42 km/hr

Speed of second bike B = 56 km/hr

Time = 30 minutes = ½ hour

**Formula:**

Distance = speed × time

**Calculation:**

Distance covered by bike A = 42 × 1/2 = 21 km

Distance covered by bike B = 56 × 1/2 = 28 km

Now, both of them are x km apart after 30 minutes

Both the bikes are moving along the right angles to each other,

we have,

⇒ 21^{2} + 28^{2} = x^{2}

⇒ 441 + 784 = x^{2}

⇒ 1225 = x^{2}

⇒ x = 35

**∴ After 30 minutes, these two bikes will be 35 km apart**