Mass is Kg
Mol is the amount of substance
m is for meters
True. I think.................
X=r-p. Maybe I don't understand, but I am assuming that you need to isolate for X? you simply subtract p from both sides.<span />
It is a solenoid.
The coil of wire looks like a spring and inside of it is a magnetic field
The spring constant is:

To calculate the <em>spring constant</em> we must remember the law for it, the Hooke's Law:

Where k is the spring constant [N/m].
So if the mass is suspended it means that its weight is equal to the elastic force (values), then we can write:

Therefore:

Now we just have to put the values and calculate:

I hope you liked it
Any doubt? write in the comments and I'll help you