Answer:

Step-by-step explanation:
The systems of equations are
Let us assume the rate of the current be c
Now actual speed against the current is (15 - c)
And, the actual speed with the current is (15 + c)
Here we applied the time formula i.e. distance by speed
Also the upstream time - downstream time = 4
Now the equations are

Answer:
24 hours/1 day
Step-by-step explanation:
hours per day is a rate which can be expressed in the form of a fraction. since there are 24 hours in one day you know that as a fraction, they are equal to 1. you can then put 24hours/1day.
4 ........................................
Put all numbers in order from least to greatest
median is the middle number
so
5,9,10,11,12,14
median = ( 10+11)/2 = 10.5
answer
C. 10.5