Answer: 4.8 s
Explanation:
We have the following data:
the mass of the raft
the force applied by Sawyer
the raft's final speed
the raft's initial speed (assuming it starts from rest)
We have to find the time 
Well, according to Newton's second law of motion we have:
(1)
Where
is the acceleration, which can be expressed as:
(2)
Substituting (2) in (1):
(3)
Where 
Isolating
from (3):
(4)
Finally:
D. Binary Stars
Well, galaxies are not stars at all rather they are collection of stars, nebulae, globular clusters and stuff like this.
Meteoroids are something entirely different.
Constellations are the pattern of stars.
So, "Binary Stars" is the Right One.
Convection cells don't work in solids.
In order for convection to happen, material with some temperature and density has to FLOW to a place where the material there has a different temperature and density.
Material doesn't FLOW in solids, only in FLuids.
That's called the wave's "wavelength" .