According to the mundell–fleming model, in an economy with flexible exchange rates, expansionary fiscal policy causes net exports to and expansionary monetary policy causes net exports to

Decrease and Increase

Explanation:

According to the Mundell–Fleming model, in an economy with flexible exchange rates, expansionary fiscal policy will cause the net exports to decrease. Expansionary fiscal policy shifts the IS curve rightwards, as a result BOP surplus created in the economy. So, exchange rate decreases to shift the BOP back to its initial position. As a result of lower exchange rate, exports falls. Hence, net exports decreases.

Expansionary Monetary policy will cause the net exports to increases. Expansionary Monetary policy shifts the LM curve rightwards, as a result BOP deficit created in the economy. So, exchange rate increases to shift the BOP back to its initial position. As a result of higher exchange rate, exports increases. Hence, net exports increases.