X = 4/15 or 0.26
First add the numbers on the left side of the equation.
0.72 = 0.8 - 0.3x
Then move the variable to the left as well.
0.3x + 0.72 = 0.8
Move the constant to the right by subtracting.
0.3x = 0.8 - 0.72
Subtract the numbers
0.3x = 0.08
Divide both sides by 0.3.
And that should yield your answer.
Hope this helps. ^^