5x - 10y = -40
-10y = -40 - 5x
y = -40 - 5x / -10

Step-by-step explanation:
Since we have given that
Time taken by steamboat makes the trip=5 hours
Time taken by yacht makes the trip =2.5 hours
Since we have also given that
the yacht is 20 knots faster than the steamboat,
So let the speed of steamboat be x
Let the speed of yacht be x+20
Now, we have given that both boats will travel the same distance ,
So,

Hence,
