Answer:
b = -1
Explanation:
Your equation is ...
(5^3)b -1 = 5^b -3
This is a mix of exponential and linear terms, and cannot be solved algebraically.
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We suspect you might mean ...
5^(3b -1) = 5^(b -3)
We can equate the exponents to find a value for b:
3b -1 = b -3
2b = -2 . . . . add 1-b to both sides
b = -1 . . . . . . divide by 2