Define scale of a graph. Explain how to scale a graph according to the given data. Mention the importance of scale on a graph.

In triangle $PQR, PQ=4\sqrt{3} centimetres, \angle P=\angle Q=30°$. Draw the triangle.

Write the coordinates of the point of intersection of the lines $x+y=5$ and $x-y=5$.

Using ruler and compass construct a triangle $ABC$ where $AB=3 \mathrm{cm}, BC=4 \mathrm{cm}$ and$\angle ABC=90°$ . Hence construct a circle circumscribing the triangle $ABC$. Measure and write down the radius of the circle.