Answer :
a = -3
nth term (u_n) = rn -3, where r = difference between each term
u_1 = -3
u_15 = 53 = 15r -3
u_15 = 56 = 15r
u_15 = 56 / 15 = r
u_n = (56/15)n - 3
nth term (u_n) = rn -3, where r = difference between each term
u_1 = -3
u_15 = 53 = 15r -3
u_15 = 56 = 15r
u_15 = 56 / 15 = r
u_n = (56/15)n - 3