Divide both sides by 4, and divide three fifths by () = 1.

Equal to 1 means that the dividend and divisor are equal, so it is three fifths in brackets.

4= three fortieth times ()

Divide both sides by 4 to get 1= 360 times ().

For multiplication, the product of a number and its reciprocal is = 1, so it is 160/3 in brackets.

Question 2: Since the ratio of the numbers of A and B is 4: 3, let A be 4x and B 3x.

(4x+3x)/2=8.4

X=2.4。

So a is 4*x=9.6.

Question 3: There are three yellow sands, so the cement is two thirds of the yellow sands and the stone is five thirds of the yellow sands.

Therefore, cement used 18*(2/3)= 12 tons.

Yellow sand used 18*(5/3)=30 tons.

So there are 6 tons of cement left;

Yellow sand increased 12 tons.