T=Tens
U=Unit
From the question... The Unit digit is twice the Tens digit
Let the Number be xy
Meaning
y is the unit number
x is the tenth Number
Can be inferred for the question that
y=2x ...........(i)
Also
If the Number is doubled x2(times 2)
"It'll be 9more than the reversed"
Now listen
if you want to express a 2digit Number...
Let's say 45...
It can be expressed as 10x4 + 5 = 45
or
66 can be expressed as 10x6 + 6 = 66
So
It'd be better if we express this our unknown number like that too
So
Let's express "xy" like "10x + y"
Hope you grab?
Now from the second statement of the question..
If The Number is doubled...It'll be 9 more than the reversed
What is the reverse of that Number??
The reverse would be "10y + x"
You can see that x and y switched places.
so
The statement said...
2(10x + y) + 9 = 10y + x (reversed)
20x + 2y + 9 =10y + x ........(ii)
Recall from our first eqn
y=2x
Now substitute y=2x into eqn ii
20x + 2(2x) + 9 = 10(2x) + x
20x + 4x +9 = 20x + x
20x - 20x + 4x - x = -9
3x = -9
x=-3
y=2x
y=2(-3)
y=-6
So The Number is 10x + y
= 10(-3) + (-6)
=-30-6
=-36
This answer obeyed the first part of the question because the unit is twice digit(2x3)
Let's check if it obeyed the second part
2[(10(-3) + (-6)] + 9 = 10(-6) + (-3)
2(-30-6) + 9 = -60-3
-63=-63
The 2nd part is also true.
So
Our Number is -36.
I'm Open to corrections if you spot any.