$30 + $30 = $60
$60 + $30 = $90
To pay back his sister the $80 he will to deposit money into his account for 3 weeks.
Since Steven would have $10 left over in his account from paying his sister all he needs now is $570.
You need to divide:
$570/$30 = 19
So Steven will need to deposit $30 into his bank account for 19 weeks to be able to buy the $580 bicycle.
Hope this Helps!!