I would try to use linkt_to
as block to gain readability
<%= link_to favorite_activity_path(activity), method: :put, :remote => true, :class => "btn favorite" do %>
<%= image_tag("Favorite 3.png", class: "act_actions", title: "Unfavorite", alt: "Unfavorite") %>
<%= activity.votes.size %>,
<% end %>
I hope that the above code works for you.