You are asked to find $a-b+c$. For what value of $x$ will $y = a-b+c$? You want the coefficient of $b$ to be $-1$, so try $x = -1$. Plugging that in, you get $y = a(-1)^2 + b(-1) + c = a-b+c$. So, looking at the graph, what is the value for $y$ when $x = -1$? That will be your answer.