Answer:
19. I
20. R
Step-by-step explanation:
The applicable rules of exponents are ...
[tex]a^{-b}=\dfrac{1}{a^b}\\\\\sqrt[n]{a}=a^{(1\!/n)}\\\\(a^b)^c=a^{bc}[/tex]
Then the expressions of 19 and 20 can be simplified as follows.
19.
[tex]343^{-2/3}=\dfrac{1}{(\sqrt[3]{343})^2}=\dfrac{1}{7^2}=\boxed{\dfrac{1}{49}}\qquad\text{matches I}[/tex]
20.
[tex]\dfrac{1}{81^{1/4}}=\dfrac{1}{(3^4)^{1/4}}=\boxed{\dfrac{1}{3}}\qquad\text{matches R}[/tex]
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Additional comment
The solution to 5 is ...
[tex]19^{1/4}=\sqrt[4]{19}\qquad\text{matches T in the first column}[/tex]
This means the second word of your final answer is "IT", not "he".
