What is the result of evaluating f of g of 12 if f(x) = sqrt(x - 3) and g(x) = x^2 + 3?

To find the result of evaluating f(g(12)), we first need to calculate g(12). Given the function g(x) = x² + 3, we substitute 12 for x:

g(12) = 12² + 3

g(12) = 144 + 3

g(12) = 147

Next, we take the result from g(12) and use it as the input for the function f. The function f(x) is defined as f(x) = √(x - 3). So now we need to evaluate f(147):

f(147) = √(147 - 3)

f(147) = √(144)

f(147) = 12

Thus, the result of evaluating f(g(12)) is 12. This is why the answer is C.