If they both have 1 week's allowance before they spend their money, then the math is like so:
Drew -
8w - 3w = y, where x is $/wk earned and y is $/wk spent and y is $ remaining
(8-3)w = y
5w = y
This is 1 week, so:
5(1) = y
5 = y
Jan:
10w - 4w = y, where x is $/wk earned and y is $/wk spent and y is $ remaining
(10-4)w = y
6w = y
This is 1 week, so:
6(1) = y
6 = y
In one week -
Otherwise they are in debt and should learn to hide out until they earn their allowance. Hopefully also learning to live within their means, because the repercussions are usually awful.