Hello please help!

Can anyone help me with the problem below:

Factorise fully the following expression:

8ax + 40cx + 3a +18c

I am told that I need to group the terms with common factors (i.e a's and c's) however when these are grouped there is no HCF between the associated numbers.

I'm sure I've missed something pretty fundamental but I just cant see it.

Any help would be great.

Thanks