Jamie saves 50 * 2 = $<<50*2=100>>100 every two weeks.
After the lunch with her mum, Jamie saves $100 - $46 = $<<100-46=54>>54 every two weeks.
Jamie saves $54 / 2 = $<<54/2=27>>27 per week.
Jamie will need 135 / 27 = <<135/27=5>>5 weeks to save enough.
#### 5