15a is non-exponential because the variable is not in the exponent
Instead, this is a polynomial function. It can also be called a power function as power functions are in the form a*x^b where 'a' and 'b' are fixed numbers.
Well, your equation y=3/SQRT(3x+4) should be rationalized, but that's not what you want.
If f(x) = 3/SQRT(x+4) and g(x) = 3x
f(g(x)) then = 3/SQRT(3x+4), but rationalizing this = 3SQRT(3x+4)/(3x+4)
We have the given I = 10^-1 and I₀ = 10^-12.
Simply plugging in the values to the equation, we have:
L = 10log(10^-1/10^-12)
L = 110 Db
The answer is D.
(I used a scientific calculator in solving for L).