at midday a ship P has position -11i+j km relative to lighthouse o. At the same time the position of boat Q is 4i-13j km relative to o. The velocities of P and Q are 3i km/h and xj km/h respectively.

if they are on a collision course what is the value of x

so i got their relative displacements which is -15i-14j

there relative velocities is 3i-xj

if i get the slope of both these they should be the same if they are on a collision course .

so -14/14=-x/3 x=2.8 the correct answer is 3. i do not see what I am doing wrong