How two to define two boolean conditions in cipher

Which of the following is a way the operating system prevents unknown or unauthorized users from accessing the system?

Acloud service provider uses the internet to deliver a computing environment for developing, running, and managing software applications. which cloud service model does the provider offer? a. iaas b. caas c. maas d. paas e. saas

Whats three fourths of 15(this is supposed to be in math but i clicked too fast)