How to find $c$ such that a given function is not discontinuous?

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I'm sorry I used a picture for the function here. I've forgotten the name of the type of function that changes behavior depending on the value of $x$, and I'm not sure how to use the math notation functionality here to display it in the form it's normally drawn in.

$$ f(x)=\left\{\begin{array}{ll}{x^{2}-7,} & {x \leq c} \\ {8 x-23,} & {x>c}\end{array}\right. $$

I need to find the value of $c$ such that $f(x)$ is continuous.

The reason I'm having trouble is because I don't know of a good way to find $c$. Could somebody please help me out?

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All you need to do is compare the two cases at $x = c$. In other words, $f$ will be continuous at $x = c$ if $c$ satisfies $$c^2 - 7 = 8c - 23.$$