One trip to school is 2 * 7 km = <<2*7=14>>14km.
In one week, Christina walks 14 km/day * 5 days/week = <<14*5=70>>70km to school.
The extra trip to her mum's friend added 2 km * 2 = <<2*2=4>>4km to her travel distance.
Her total distance was thus 70 km + 4 km = <<70+4=74>>74 km
#### 74