How Are Expressions Derived from Previous Equations in Mathematical Problems?

[skku]

Problem number 1:
How the author has achieved expression 7 and 8 by using 6?

Problem number 2:
How the author has achieved expression 13,14 and 15 by using 12?

Thanks in advance

 

[mfb]

Just arithmetics. Divide (6) by B*η, put both sides in an exponent (2^...), simplify, rename γ to γ_thD.
To get (8), replace R by 2R.

I think the second problem needs some formulas not given in the image.