Just divide.

0.583333. . .
^ This is the thousandths place
Look at the number after that, if it's 5 or more we round up, if it's 4 or less we round down.
It's 3, so we round down to 0.583.
.4 as a percentage is 40%
Subtract 2x from both sides then you’d have -7x+4=16 Then you subtract 4 from both sides and you’d get -7x=12. Next you divide both side by -7 so x=1.75 rounded to the nearest hundredth.
..... 40.5 ...............