To form the usted form of the imperative of the regular -ar verb hablar, you need to follow these steps:
1. Take the present tense form of the verb hablar that corresponds to the usted form, which is "usted habla."
2. Remove the "-a" ending from the verb, which leaves you with the stem "habl-."
3. Add the appropriate ending to the stem, which for the usted form is "-e."
4. The final result is "hable," which is the usted form of the imperative of the verb hablar.
So, to summarize: To form the usted form of the imperative of the regular -ar verb hablar, you take the present tense form "usted habla," remove the "-a" ending, add the "-e" ending, and get "hable."