She walks .5 miles to school and back 4 times a day so that's .5*4 = <<.5*4=2>>2 miles
She walks 2 miles a day for 5 days so that's 2*5 = <<2*5=10>>10 miles
Over 4 weeks of walking 10 miles per week she walks 4*10 = <<4*10=40>>40 miles
#### 40