Write formal commands using the information provided.(a) por favor, / no / estar / enojado / (usted)(b) conocer / (ustedes) / nuestro / productos / y / aprender / usarlos(c) ser / flexible / (ustedes) / y / darme / más / tiempo(d) venir / (usted) / mi / casa / las / seis / tarde

These are the answers:

A. Por favor no esté (usted) enojado.

B. Conozcan (ustedes) nuestros productos y aprendan a usarlos.

C. Sean (ustedes) flexibles y denme más tiempo.

D. Venga (usted) a mi casa a las seis de la tarde.  

Explanation: Just to elaborate a little bit on the answer, it can be added that the so-called "imperativo" mood is used in Spanish to give an order or to make a petition or a wish. The imperative form is only available for the second person ("tú" in singular and "vosotros" in plural). For the rest of the persons, such as "usted" and "ustedes," it is necessary to use the subjunctive mood.  

answer: the answer is b. se quejan because it's in the plural form.