After 13.6L of water is poured into the tank, the water depth in the tank is x.

x:50= 13.6:30

Get x=22cm.

After the iron is put in, it is 25cm, so the volume of the cube is V1= 30 * 20 * (25-22) =180 cm?

If each ticket is reduced by X yuan, there will be

(50-x)* 1.5 = 50( 1+ 1/5)

Get x= 10.

So the price of each ticket is reduced 10 yuan.

3，B

4, d, because a and b are not necessarily integers.

5，C