“[U]nder California law, exemptions from statutory mandatory overtime provisions are narrowly construed. Moreover, the assertion of an exemption from the overtime laws is considered to be an affirmative defense, and therefore the employer bears the burden of proving the employee’s exemption.” Ramirez v. Yosemite Water Co. (1999) 20 Cal.4th 785, 794–795 (internal citations omitted). California Labor Code section 510(a) requires employers to pay overtime compensation—that is, to compensate its employees at a higher rate for hours worked over eight in a day or forty in a week. Lab. Code § 515(a) gives the Industrial Welfare Commission (“IWC”) the authority to establish exemptions from the overtime pay requirement. The IWC promulgated Wage Order No. 4, which relates to “professional” and “technical” employees. Cal. Code Regs., tit. 8, § 11040. The wage order establishes four exemptions from the overtime requirement: the (1) executive, (2) administrative, (3) professional, and (4) computer professional exemptions. Id. at subd. 1(A). Pursuant to the Wage Order, in order to be exempt, an employee must perform exempt duties more than fifty-percent of the time.