Hide title in Merlin Theme on posts and pages only

Your theme correctly uses the body_class function, which you can see by looking at the body tag. This means CSS classes are being added such as page or post that you can work with.

e.g.

body.page .entry-title { display: none; }

There are many other CSS classes that may be useful to you, I suggest you browse your website with the developer tools turned on to see what CSS classes are available for styling