Do you mean this number:

?
The we have to simplify the fraction part, since the nominator is bigger than the denominator.
How many denominators fit into the nominator? 20: 4=5
5! so

is simply 5 and we can add it to the main number:
175+5=180
7 is the leases common I’m pretty sure
la respuesta es 454 espero que te haya ayudado aunque sea un poquito :D
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