Explanation:
the graph tells us :
she traveled the first 2 hours altogether 160 km.
then she stayed "still" somewhere (probably at a rest station) for 1 hour.
and then she traveled 3 hours at 60 km/h (kilometers per hour).
during these last 3 hours the given speed tells us that she was travelling 60 km for every hour.
so, in 3 hours she traveled
3 × 60 = 180 km
therefore, d is the total distance she traveled :
first 160 km
then 0 km
then 180 km
d = 160 + 0 + 180 = 340 km