The amount of money Diana earned in August is 3 * $150 = $<<3*150=450>>450.
The amount of money Diana earned in September is 2 * $450 = $<<2*450=900>>900.
The total amount of money Diana earned over the three months is $150 + $450 + $900 = $<<150+450+900=1500>>1500.
#### 1500