Answer:520; 240
Explanation:
a. 13, 26, 39, 52,......
a = First term = 13
d = common difference = 26 - 13 = 13
40th term = a + (n - 1)d = a + (40-1)d = a + 39d
= 13 + (39 × 13)
= 13 + 507
= 520
b. 6, 12, 18, 24,.......
a = First term = 6
d = common difference = 12 - 6 = 6
40th term = a + 39d
= 6 + 39(6)
= 6 + 234.
= 240