To find the greatest common factor (GCF) of the expression \( 18j + 27 \), we can start by finding the GCF of the coefficients of the terms in the expression.
- The coefficients are 18 and 27.
- The factors of 18 are: 1, 2, 3, 6, 9, 18.
- The factors of 27 are: 1, 3, 9, 27.
The common factors of 18 and 27 are 1, 3, and 9. The greatest of these is 9.
Thus, the GCF of \( 18j + 27 \) is \( \boxed{9} \).