1. The problem is to express $Z$ given the formula $Z=1-\frac{I}{2}$. 2. Here, $1$ is a constant term, and $\frac{I}{2}$ means half of the variable $I$ is subtracted from 1. 3. If you want to find $Z$ for a particular value of $I$, substitute that value into the formula and compute $Z$. 4. For example, if $I=4$, then $$Z=1-\frac{4}{2}=1-2=-1.$$