I need help with making plural of thise sentences:

1.Una muchacha guapa-
*I know that that I am not using los/las and I need tu change muchacha to muchachas but I don’t know if I had to add -s to guapa as well or nah same problem with sentence number. 2

2.La lengua importante-
* I know I have to start with las lenguas but again should I change importante as well or leave it alone

And this is my problem -if I should change adjective or no.
Pls help asap.