The two circles below are externally tangent. A common external tangent intersects line $PQ$ at $R.$ Find $QR.$
The two circles below?
\(\overline{PQ}=\sqrt{(R+r)^2-(R-r)^2}=\sqrt{R^2+2Rr+r^2-R^2+2Rr-r^2}\\ \color{blue}\overline{PQ}=2 \sqrt{Rr}\)
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+2115 
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