Your order total should be $40 + Tax
YMMV at this point:
If you want, you could sign up for their Mobile Insider to get $10 off your $50 purchase, then buy 3 jeans, which total to be $60, apply coupon = $50.
I haven't try this yet,
Or you could buy 5 jeans = $100, they have $30 off promotion, which makes it $70, then apply the $10 coupon. So total should be $60 + Tax. But I don't know if they allow to stack coupons