Roberta's bag costs $45 - $17 = $<<45-17=28>>28.
Roberta spend $28 / 4 = $<<28/4=7>>7 on lunch.
Roberta spend 45 + 28 + 7 = <<45+28+7=80>>80 in total.
Roberta has $158 - 80 = $<<158-80=78>>78 left.
#### 78