Answer:

Step-by-step explanation:
First ship starts at Noon with speed 20 Knots towards West
now we know that 2nd ship starts at 6 PM with speed 15 Knots towards North West
so after time "t" of 2nd ship motion the two ships positions are given as


now we can find the distance between two ships as

now we have


now we will differentiate it with respect to time

here we know that

so we have

now we have

