tolong bantu jawab please nmr 15

C
a. S1 = 2(5³ - 5) = 240
b. S1 = 2(5² - 1) = 48
c. S1 = 2(5² - 5) = 40
d. S1 = 2(5° - 1) = -2
e. S1 = 2(5° - 5) = -8