Question

A builder needs 6.5 cubic metres of concrete for a job. This table shows the mixture for the concrete.

Answer 1

If the four parts sand means 4 cubic meters of sand per 13 cubic meters of concrete, you can you can multiply 4/13 by 6.5 to get 2 cubic meters of sand.

Let me know if I misinterpreted the question so that I can try to fix it.  I hope this helps