Помоги упростить выражения: 11^k : 11^4 * 11^{k+1}

Конечно, сейчас помогу упростить выражения! 7) $11^k : 11^4 \cdot 11^{k+1} = 11^k : 11^{4 + k + 1} = 11^k : 11^{k+5} = 11^{k - (k+5)} = 11^{k - k - 5} = 11^{-5} = \frac{1}{11^5}$$ 8) $20^{10} : 20^t \cdot 20^{3+t} = 20^{10} : 20^{t + 3 + t} = 20^{10} : 20^{2t+3} = 20^{10 - (2t+3)} = 20^{10 - 2t - 3} = 20^{7 - 2t}$$ 9) $(-9)^{20t} : (-9)^{t+5} : (-9) = (-9)^{20t} : (-9)^{t+5} : (-9)^1 = (-9)^{20t} : (-9)^{t+5+1} = (-9)^{20t} : (-9)^{t+6} = (-9)^{20t - (t+6)} = (-9)^{20t - t - 6} = (-9)^{19t - 6}$$ 10) $(\frac{1}{4})^{3k} : (\frac{1}{4})^k = (\frac{1}{4})^{3k - k} = (\frac{1}{4})^{2k}$$ 11) $(-\frac{1}{9})^{5t-2} : (-\frac{1}{9})^{5t} = (-\frac{1}{9})^{5t-2 - 5t} = (-\frac{1}{9})^{-2} = (-9)^2 = 81$$ 12) $2,1^{t+3} \cdot 2,1^{6t} : 2,1^{4t+3} = 2,1^{t+3+6t} : 2,1^{4t+3} = 2,1^{7t+3} : 2,1^{4t+3} = 2,1^{7t+3 - (4t+3)} = 2,1^{7t+3 - 4t - 3} = 2,1^{3t}$