Resposta:
[tex] {3}^{20} \\ [/tex]
Explicação passo-a-passo:
[tex] \frac{ {3}^{23} + {3}^{21} - {3}^{22} }{21} = \\ \frac{ {3}^{21} \times ( {3}^{2} + 1 - 3) }{3 \times 7} = \\ {3}^{20} \times \frac{9 + 1 - 3}{7} = \\ {3}^{20} \times \frac{7}{7} = {3}^{20} [/tex]
