in doing sth ( in 可以省略）
Yeah,I really have a hard time believing she is already 60.
是啊.我确实很难相信她已经60岁了.
.But they have a hard time equating plural marriage with those evils.
但是他们很难把这种多妻婚姻与上面说的那些坏事联系起来.
Why do leopards have a hard time hiding?
为什么美洲豹要藏起来很困难?
问题补充：
是不是have a hard time 接with sth?
没错.如：
have a hard time with sb.
和某个人的关系处的特别不好