He needs to replace 30*10=<<30*10=300>>300 ball bearings
The normal price is 300*1=$<<300*1=300>>300
Because of the sale he only has to pay 300*.75=$<<300*.75=225>>225
He then gets a discount which shaves another 225*.2=$<<225*.2=45>>45 off the price
That means he only pays 225-45=$<<225-45=180>>180
So he saved 300-180=$<<300-180=120>>120
#### 120