Concept:On Friday, the obligatory 4-rak'ah Dhuhr prayer is replaced by the 2-rak'ah Jumu'ah prayer.This lowers the total obligatory rak'ah from 17 to 15.Explanation:The normal daily obligatory prayers total 17 rak'ah.Fajr has 2 rak'ah, Dhuhr has 4, Asr has 4, Maghrib has 3, and Isha has 4.On Friday, Jumu'ah replaces Dhuhr in the obligatory prayers.Jumu'ah consists of only 2 rak'ah, while Dhuhr has 4 rak'ah.Therefore, the total becomes 17−4+2=15 rak'ah.So Friday's obligatory prayers are Fajr 2, Jumu'ah 2, Asr 4, Maghrib 3, and Isha 4.Adding them gives 2+2+4+3+4=15 rak'ah.Answer:D. 15