In one week he will have saved 20+10=<<20+10=30>>30 dollars
In two weeks he will have saved 30+10=<<30+10=40>>40 dollars
In three weeks he will have saved 40+10=<<40+10=50>>50 dollars
At the end of week four, he will have saved 50+10=<<50+10=60>>60 dollars
#### 60