What is the sum of the two solutions of the equation $x^2-4x-45=0$ ?

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Note, you can solve this by graphing it in the calculator and finding $x$-intercepts. Alternatively, factoring:

$$x^2-4x-45=0$$ $$(x-9)(x+5)=0$$ $$x=9 \text{ and } x=-5$$ $$9+(-5) = \boxed{4}$$