(a) 
The relationship between frequency and wavelength of an electromagnetic wave is given by

where
is the speed of light
is the frequency
is the wavelength
In this problem, we are considering light with wavelength of

Substituting into the equation and re-arranging it, we can find the corresponding frequency:

(b) 
The period of a wave is equal to the reciprocal of the frequency:

And using
as we found in the previous part, we can find the period of this wave:

Answer:
The object will have an upward acceleration
Explanation:
Let's consider the forces applied on the box. We have only two forces:
- The applied force of push,
, downward
- The force of gravity,
, (also known as weight of the object), downward
Therefore, the net force on the box is:

Here, we know that force applied is equal or greater than the weight, so

And therefore the net force is greater than zero:
(1)
According to Newton's second law of motion, the net force on the box is equal to the product between its mass and its acceleration:

where
m is the mass of the box
a is its acceleration
Given (1), this means that

Therefore, the box will have an upward acceleration.
In this case force example we have:

So the mass of the box is

So the net force is

And the acceleration is

Density is mass over volume:

In your case, mass is 48 grams and volume is 12cm^3
If you put that into the equation, you will get your density:
The initial force of the throw overcomes gravity quite easily. Then, gravity begins to bring it back down to earth, making a curved path.