Let's go to the sports stadium on Friday.
= Shalll we go to the sports stadium on Friday?
= Why not go to the sports stadium on Friday?
= Why don't we go to the sports stadium on Friday?
= What/How about (us/our) going to the sports stadium on Friday?
注：（ ）表示可以省略不写；/ 表示可以任意选用其一.