CAT Exam Model Paper 1 with solutions for free online practice

The separation between the ship and the seaplane is 18 miles. And since the two are travelling in the same direction, the relative speed would be 9 times the speed of the ship (If speed of ship is x miles/hour, speed of seaplane would be 10x and 10x − x = 9x).
Hence to catch up with the ship the seaplane would take $\frac{18}{9\mathrm{x}}=\frac{2}{\mathrm{x}}$ hours. Now, the ship covers x miles in an hour, so in $\frac{2}{\mathrm{x}}$ hours it would cover 2 miles. So, when the seaplane catches up with the ship, it would be 18 + 2 = 20 miles from the shore.