Thans for helping. I think, I have leads for the second one.

The solution shows this:

3^(2c+1)=28*(3^c)-9

3^(2c)*3^1 = 28*3^c - 9

3(3^c)^2 - 28(3^c) + 9 = 0

**let 3^c = x**

3x^2 - 28x + 9 = 0

(3x - 1)(x - 9) = 0

x = 1/3 or x = 9

if x = 1/3

3^c= 1/3 = 3^-1

**c = -1**

if x = 9

3^c = 9 = 3^2

**c = 2**