Let's say a pile is x tons and b pile is y tons.

x+y = 164( 1-20%)* y = 20% y+x- 12

Simplify the second formula: 80% y = 20% y+x-12 60% y = x-12 x = 60% y+12.

Then x=60%y+ 12 is brought into the first formula.

Get: y = 95+ 12+y = 164 of 60%y, and then bring it into the original formula to get x=69.

That is, pile A is 69 tons and pile B is 95 tons.

The second question:

This building is x meters high.

(x+8/3)*2=(x+3/2)*3

2x+ 16/3+=3x+9/2

X=5/6 (building height) means rope length: (5/6+8/3)*2=7 (meters).

The third question:

Who contains salt in the original:

500*3.2%= 16 (gram salt)

The amount of salt is constant, and the water is reduced, so when the salt accounts for 8%, the salt water is heavy:

16 divided by 8%=200 (g) (saline)

So it evaporated:

500-200=300 (grams of water)

Answer: To evaporate 300g of water, the idea is that the weight of salt (16) remains unchanged.

Since you have asked the general social equation, you can certainly understand this step.

You can also ask me the formula.