3x - 50 = -20
Add 50 to both sides
3x = 30
x = 10
The number is 10
Let X and Y be the digits.
If a two-digit number is written XY, then its value is 10x+y.
When the digits of the number are interchanged, it's YX, and its value is 10y+x.
The sum of the digits is 12.
The number formed by interchaning the digits is 54 more than the original number.

The digits X and Y are 3 and 9, so the original number is 39.
Let's simplify step-by-step.
−3x2−5x2(4x3−x2)(2)
Distribute:
=−3x2+−40x5+10x4
Answer:
=−40x5+10x4−3x2