There are 3 series, you have to find values of a, b and c and then use them to solve the following and find the value of k.

50% of b – 14.28% of a + c = k

(i) 221, 364, 561, 816, a, 1540

(ii) 160, 329, b, 979, 1508, 2349, 3310

(iii) 36, 80, 150, 252, 392, c