Here is a graph showing a straight line. It is not drawn accurately. The points \((2,3)\) and \((8,8)\) lie on the line. Another point, \((4,a)\), also lies on the line. Can you work out the value of \(a\)?

How many different ways can you find to do this?

There are no triangles in this graph. Perhaps we could draw some in and hunt for something nice among them?

Alternatively, perhaps we could find the equation of the line?

Then again, maybe we could just calculate the gradient of the line…