I know it may be difficult, but I am sure that you will be able to do it, so I would really appreciate it if you could do this.
"I know it may be difficult"=「これが難しいかもしれないとは分かっています」
"but I am sure that you will be able to do it"=「でも、あなたなら出来ると私は確信しています」
"so I would really appreciate if you could do this"=「なので、あなたがこれをしてくれると、とてもありがたいです」