Hello!
First, you'd want to add 4 to each side. For example, you'll want to add 4 to 4 and 13. After you've done that the equation should now look like this
3x=17
Next, you'll need to divide each side by 3, meaning you'll divide 17 and 3 by 3. Your equation will now look like...
x=5.6 repeating (5.66666...)
Your answer will be x=5.6
I ope this helps!