Ineed finding the whole question, i'm not sure if what i've done already if correct,

Median of 15

(14 + b) / 2 = 15
14 + b = 15 * 2
14 + b = 30
b = 30 - 14
b = 16

range of 30
 c - a = 30c = 30 + a

mean of 18
(a + 8 + 14 + 16 + 26 + c) / 6 = 18
(a + 8 + 14 + 16 + 26 + (30 + a)) / 6 = 18
(2a + 94) / 6 = 18
2a + 94 = 18 * 6
2a + 94 = 108
2a = 108 - 94
2a = 14
a = 14/2
a = 7

c - a = 30
c - 7 = 30
c = 30 + 7
c = 37

check..
7,8,14,16,26,37
median = (16 + 14) / 2 = 30/2 = 15 ...correct
range = 37 - 7 = 30...correct
mean(average) = (7 + 8 + 14 + 16 + 26 + 37) / 6 = 108/6 = 18...correct

so a = 7, b = 16, and c = 37