` a) ` ` \frac{16}{2^n} = 2 `
` => 2 . 2^{n} = 16 `
` => 2^{n + 1} = 2^4 `
` => n + 1 = 4 `
` => n = 3 `
` b) ` ` \frac{(-3)^n}{81} = -27 `
` => (-3)^n = -27.81 `
` => (-3)^n = (-3)^3 . (-3)^4 `
` => (-3)^n = (-3)^7 `
` => n = 7 `
` c) ` ` 8^n : 2^n = 4 `
` => 2^{3n} : 2^n = 2^2 `
` => 2^{3n - n} = 2^2 `
` => 2n = 2 `
` => n = 1 `