I am doing something wrong when I work this question. Can someone show me the steps. I have the answer. x<5.189

Question

The sum of the costs in parts a and c is less than $120. Write and solve an inequality to determine the possiblities for the number of compact disks Merle purchased.

10.5x + 8(x+3)< 120

I know the answer is x< 5.189
Here is how I did it but I believe it is wrong.
10.5x + 8(x+3)<120
10.5x + 8x+3<120
18.5x + 3< 120
18.5x + 3-3<120-3
18.5x<117
X<6.324(wrong)
Help please

ere is how I did it but I believe it is wrong.
10.5x + 8(x+3)<120
10.5x + 8x+3<120 error here, should b
10.5x + 8x+24<120


Thank you so much.