Marco and his dad went strawberry picking. Together they collected strawberries that weighed 36 pounds. On the way back Marco ' dad lost 8 pounds of strawberries. Marco's strawberries now weighed 12 pounds. How much did his dad's strawberries weigh now?
Let's say Marco's dad's strawberries weighed x pounds. 

Then we know that: 

x + 12 = 36 

x = 24 

So Marco's dad's strawberries weighed 24 pounds.