5.8-0.3(x-6.0)=0.5x ... (multiply out to remove the parenthesis)
5.8-0.3x+1.8 = 0.5x ... (add like terms to simplify)
7.6-0.3x = 0.5x ... (add 0.3x to both sides to keep unknowns to one side)
7.6 = 0.8x ... (divide both sides by 0.8 to get x alone)
x = 9.5
Now you can check the answer:
5.8-0.3(9.5-6.0) = 0.5(9.5)
4.75 = 4.75