The error is in the second step they subtracted 3 from both sides but it was a 3x, which you can not do.
Correction.
9x+18+3x=1
12x+18=1
12x=-17
x=-17/12
X/12=(2 1/3)/5 note that 2 1/3=7/3
x/12=(7/3)/5
x/12=7/15 multiply both sides by 12
x=84/15
x=28/5
x=56/10
x=5.6
