What's at the bottom of a black hole?

All matter in a black hole is crushed into a single point at the center called singularity. 

$17.99 * 0.2 = $3.60 (amount taken off for each shirt)

$17.99 - $3.60 = $14.39 (per shirt)

40 / 14.39 = 2.779 (round to 3)

You'd have to buy 3 shirts in order to use your coupon.

($14.39 * 3 = $43.17, in order to get $10 off you'd need to spend at least $40)