If f(x) = x + 2 and g(x) = x - 2, what is (f · g)(5)?

The notation $(f\cdot g)(5)$ means the product $f(5)\cdot g(5)$. Compute $f(5)=5+2=7$ and $g(5)=5-2=3$. The product is $7\cdot3=21$, choice B. Using the product function, $(x+2)(x-2)=x^2-4$, and at $x=5$ that is $25-4=21$. Choice A ($10$) adds $f(5)$ and $g(5)$, which is $(f+g)(5)$. Choice C ($25$) is $5^2$, forgetting the $-4$. Choice D ($3$) is $g(5)$ alone. A dot between functions means multiplication of their outputs. The two methods agree, so the answer is reliable.