$$6-2=4$$  $$6+4=10$$  $$7\times 10=70$$ 
Joann and Sana are practicing writing stories. Joann writes $6$ stories each day, and she writes $2$ more than that of Sana each day. How many stories do they write in total in one week? 
Options:
[1] $$14$$ 
[2] $$28$$ 
[3] $$42$$ 
[4] $$70$$ 
[5] $$98$$ 