In each case, you can start by taking the antilog.
21. x = 4^(3/2)
x = 8
22. 81 = x^(4/3)
81^(3/4) = x = 27
24. 2x - 3 = 6^0
2x = 4 . . . . . add 3
x = 2
25. 5 - x = 16^(1/2)
5 - 4 = x = 1
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You're using the relationship of logarithms:
[tex]\log_a{b}=c\,\Longrightarrow\,b=a^{c}[/tex]
