Aye me plz : )

given the following sequence, find the 15th term: 3, 1, –1, –3, –5, . .

a. –28
b. –25
c. –33
d. –21

Its a arithmetic progression with d = 1-3 = -1-1= -2
hence a15 = a1 + 14d
hence a15 = 3 + 14(-2) = -25 
here a1 represent first term , d represent common difference