For two linear equations a1x + b1y + c1 = 0 and a2x + b2y + c2 = 0 to have no solution:

a1/a2 = b1/b2 ≠ c1/c2

Here,
a1 = 3, b1 = −k, c1 = 8
a2 = 9, b2 = −18, c2 = 20

So,
3/9 = (−k)/(−18)

1/3 = k/18

k = 6

Now check constants:
8/20 = 2/5

Since 1/3 ≠ 2/5,
Condition is satisfied.

Therefore, k = 6.