15) For a certain arithmetic sequence, a3 = 57 and d = 4. What is a rule for the nth term of the sequence? a) a, =-63-4n b) a, =-59-4n c) a, =-63+4n d) a, =-59+4n For problems 16 - 20, write a rule for the nth term of the arithmetic sequence that has the two given terms. 16) as = 39, a14 = 79 17) ag = -10, a20 = -58 18) a9 = 89, a15 = 137 19) a2 = 17, an = 35 20) as = 15, a9 = 24 21) For a certain arithmetic sequence, as = -6 and a13 = -48. What is a rule for the nth term of the sequence? a) a, =18+6n b) a, =30-on c) a, =-6+24n d) a, =-36-on 22) A marching band is arranged in 7 rows. The first row has 3 band members and each row after the first has 2 more band members than the row before it. Write a rule for the number of band members in the nth row