Lady walks in the store and steels $100.00 from register then buys $70.00 worth of food how much did the owner loose

$30 of goods were stolen

If the lady steals $100 from the store, and buys $70 worth of food from the same store she stole the money from, then the owner loses $100.

The owner loses the initial $100, but gets back $70, so he is losing $30 of cash that the lady keeps.

The woman gets $70 of food for free without technically adding any extra money into the store, so the owner loses an additional $70 (of food.)

Again, in total, the owner loses $100.

Agc and bgd are vertical angles