Answer:
x = 7
Step-by-step explanation:






Hope this helps
I think 20 hope that helps
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