Answer:
36
Step-by-step explanation:
Here is the correct and complete question: The units digit of a two-digit number is twice the tens digit. If the digits are reversed, the new number is 9 less than twice the original number. What is the original number?
 
Lets assume the original number be"10y+x". (x is unit digit and y is 10th digit)
∴ if number is reversed then resulting number be "10x+y".
As given: x= 2y 
         and 
Now, solving the equation to get original number.
 
Distributing 2 to 10y and x, then opening the parenthesis.
⇒ 
subtracting by (2x+y) on both side.
⇒ 
subtituting the value of "x", which is equal to 2y.
∴ 
⇒ 
subtracting both side by (16y-9) 
⇒ 
cross multiplying 
We get, 
y=3
∵x= 2y

∴ x= 6
Therefore, the original number will be 36 as x is the unit number and y as tenth number.
 
        
             
        
        
        
So we know that there are 1000 mL in 1 L. We can set up an equation that allows us to solve for how many bottles are needed in order to empty the 30 L tank:

This equation then allows us to cancel out the units of mL and L, leaving us with how many bottles are needed per tank. Then we multiply straight across to give us:

The question asks us to round up to the next whole number, so 
it would take 86 bottles to empty one 30 L tank.
 
        
        
        
The answer is 3.16 
explanation:
.