1. **State the problem:** We need to find an expression for "one third of x then add 4". 2. **Write the expression:** "One third of x" means $\frac{1}{3}x$. 3. **Add 4 to the expression:** So the full expression is $\frac{1}{3}x + 4$. 4. **Final expression:** $$y = \frac{1}{3}x + 4$$ This means for any value of $x$, you multiply it by $\frac{1}{3}$ and then add 4 to get $y$.