If f(x) = x² + 1 and g(x) = 2x - 3, what is (f - g)(4)?

The notation $(f-g)(4)$ means $f(4)-g(4)$. Compute $f(4)=4^2+1=17$ and $g(4)=2(4)-3=5$. Then $17-5=12$, choice B. Choice C ($17$) is $f(4)$ alone, with $g(4)$ never subtracted. Choice A ($10$) comes from using $g(4)=7$ by adding $3$ instead of subtracting it. Choice D ($22$) adds the two functions, $17+5$, so it computes $(f+g)(4)$ rather than $(f-g)(4)$. You can also form the difference first: $(f-g)(x)=x^2+1-(2x-3)=x^2-2x+4$, and at $x=4$ that equals $16-8+4=12$. Be careful to distribute the minus sign across all of $g(x)$.