What was the change in the net revenue from EMS between 2018 and 2019?
{"Net revenue -- EMS": {"2019": 15430529, "2018": 12268600, "2017": 11077622}, "Net revenue -- DMS": {"2019": 9851791, "2018": 9826816, "2017": 7985499}, "Net revenue -- ": {"2019": 25282320, "2018": 22095416, "2017": 19063121}}
net_revenue_ems_2019 = df["Net revenue -- EMS"]["2019"]
net_revenue_ems_2018 = df["Net revenue -- EMS"]["2018"]
answer = net_revenue_ems_2019 - net_revenue_ems_2018