Question 1069899
x, volume of 40% silt
12-x, volume of pure 100% silt


{{{(40x+100(12-x))/12=85}}}



Why dividing by 12?


Remind yourself of what percent mean?
Numerator is expression for HOW MUCH silt.
Denominator is HOW MUCH VOLUME OF soil.



<a href="https://www.youtube.com/watch?v=-REjxT9KCzQ">Example of the same type - one variable for two-part mixture</a>