First, let's subtract three from both sides so that x is isolated:
5x + 3 - 3 = 4 - 3
5x = 1
Divide both sides by 5 so that x is now completely isolated:
x = [tex]\frac{1}{5}[/tex]
This can also be written as 0.2, in case the question prompted for decimal form.
Good luck!
