Account A starts with $100 and has $20 added to it each week. Account B starts with $250 and has $10 added to it each week. The amount of money in Account A after $w$ weeks can be represented by $A=100+20w$, and the amount of money in Account B after $w$ weeks can be represented by $B=250+10w$. After how many weeks will the amount of money in Account A be equal to the amount of money in Account B?