All fossil fuels are formed deep underground. they are all nonrenewable energy
The reason is because the force due to the acceleration from gravity is constant. It's the same as the typical "dropping a bowling ball and feather (with no air resistance) at the same time". Gravity acts on all object with the same acceleration regardless of physical properties.
Let us assume the upstream rowing rate of Alicia = x
Let us assume the downstream rowing rate of Alicia = y
We already know that
Travelling time = Distance traveled/rowing rate
Then
6/(x + 3) = 4/x
6x = 4x + 12
6x - 4x = 12
2x = 12
x = 6
Then
Rowing rate of Alicia going upstream = 6 miles per hour
Rowing rate of Alicia going downstream = 9 miles per hour.
Current will be

now just pluf in the values and Voila..