Marco and his dad went strawberry picking. Together they collected strawberries that weighed w pounds. On the way back Marco ' dad lost x pounds of strawberries. Marco's strawberries now weighed y pounds. How much did his dad's strawberries weigh now?
First, we know that Marco and his dad went strawberry picking. Together, they collected strawberries that weighed w pounds. 

Next, we know that on the way back, Marco's dad lost x pounds of strawberries. This means that the weight of the strawberries that Marco's dad had left was w - x pounds. 

Lastly, we know that Marco's strawberries now weighed y pounds. This means that the weight of the strawberries that Marco's dad had left was w - x - y pounds.