If Madeline sells one dress at a discount of 10% of the usual price, she will make a profit of $150. If she sells it at a discount of 40%, she will still make a profit of $30. Find the cost price of the dress.

40% - 10% = 30%

$150 - $30 = $120

30% --> $120

1% -->$4

90% --> $360

$360 - $150 = $210 (Cost price of the dress)