P, Q, and R are located in a flat region of a certain state. Q is x miles due east of P and y miles due north of R. Each pair of points is connected by a straight road. What is the number of hours needed to drive from Q to R and then from R to P at a constant rate of z miles per hour, in terms of x, y, and z ? (Assume x, y, and z are positive.)
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A$$\sqrt{(x^2+y^2)}\over{z}$$
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B$$x+{{\sqrt{x^2+y^2}}}\over{z}$$
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C$$y+{\sqrt{(x^2+y^2}}\over{z}$$
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D$${z}\over{x}+\sqrt{(x^2+y^2)}$$
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E$$z\over{y}+\sqrt{(x^2+y^2)}$$