We know that, distance between two parallel planes:

Ax + By + Cz + D₁=0…… (1) and Ax + By + Cz + D₂=0…… (2) is given by,

Here, the two parallel planes are given as,

2x–y + 3z=4 i.e. 2x–y + 3z - 4=0 …………… (3)

and 2x–y + 3z=18 i.e. 2x–y + 3z - 18=0 ………… (4)

Comparing equation (3) with equation (1) and equation (4) with equation (2) we get,

A=2, B= - 1, C=3, D₁= - 4 and D₂= - 18.

So, the distance between the given two parallel planes are,

Hence, the distance between the parallel planes 2x–y + 3z=4 and 2x–y + 3z=18 is .