Is there something wrong with the line beginning with echo? I'm getting this error but I'm not sure how I can change it: Parse error: syntax error, unexpected '.' on line 74
while ( have_rows('stills') ) : the_row();
    // display a sub field value
    echo '<li><img src="' . the_sub_field('still'); . '" alt="<?php the_sub_field('project_name'); ?>-still"></li>'
endwhile;
I changed it to this but it's still not outputting correctly: echo '<li><img src="' . the_sub_field('still') . '"></li>';
Also, if this isn't the area to ask for help on these types of questions, where can I ask?
Edit: Tried satyr607's solution and this is how it's outputted.
<div class="project-stills">
    <h3>Stills</h3>
    http://localhost/wordpress/wp-content/uploads/2014/12/17.jpg
    <li><img src="" alt="-still"></li>
</div>
 
    