1. **State the problem:** We are given the formula for the standard error or margin of error as $\sigma= \frac{2}{U-L} \times z_n$, where $U$ and $L$ are known values. 2. **Understand the variables:** $U$ is the upper bound, $L$ is the lower bound, and $z_n$ is a z-score value corresponding to the confidence level. 3. **To solve for $\sigma$, substitute the known values of $U$, $L$, and $z_n$ into the formula:** $$\sigma= \frac{2}{U-L} \times z_n$$ 4. **Simplify the expression by computing $U-L$, then dividing 2 by this result, and finally multiplying by $z_n$.** 5. **Example:** If $U=10$, $L=4$, and $z_n=1.96$, then $$U-L=10-4=6$$ $$\sigma= \frac{2}{6} \times 1.96= \frac{1}{3} \times 1.96 = 0.6533$$ 6. **Answer:** The value of $\sigma$ is $0.6533$ in this example. Simply plug in your given values of $U$, $L$, and $z_n$ and follow these steps to compute $\sigma$.