It seems you're asking to determine a value $c$ such that a certain probability holds for a standard normal variable $Z$. To solve this type of problem, we'll need the exact probability statement, which typically involves the cumulative distribution function (CDF) of the standard normal distribution.

For example, a typical question might be:

"Find $c$ such that $P(Z \leq c) = 0.975$."

In this case, you would look for the value of $c$ that corresponds to a cumulative probability of 0.975 using a standard normal distribution table or calculator.

Could you clarify what specific probability or condition for $Z$ is given? This would help me compute the precise value of $c$.