It's really simple...let's walk through it.
The original equation...
F = 1 / (2pi sqrt(LC))
If we were to put this equation into words, it would say -
Frequency is the reciprocal of 2pi times the square root of the product of L and C
So the first thing we need to do to rearrange is reciprocate the frequency itself -
L = 1 / F
Now we need to divide the frequency by 2pi -
L = (1/F) / 6.28
Once we've done that, we now need to square it to reverse the square root function -
L = ((1/F) / 6.28) ^ 2
Then the last thing we do is divide this by the value of C -
L = ((1/F) / 2pi) ^ 2 / C
Once you've solved for L, you can then perform the F = 1 / (2pi sqrt(LC)) to check your work.
Make sense?