Answer:
21 in.
Step-by-step explanation:
The radius is half of the diameter. The diameter (as shown) is 42 inches. Divide that by two to get 21 in.
The equivalent expression of
is 
<h3>How to determine the equivalent expression?</h3>
The logarithmic expression is given as:

The law of logarithm states that:
log(a) - log(b) = log(a/b)
This means that the expression can be split as:

Hence, the equivalent expression of
is 
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The answer to -3-8+(-4) is -15