Dalvin runs a farm stand that sells strawberries and blueberries. Each pound of strawberries sells for $2 and each pound of blueberries sells for $3.50. Dalvin sold twice as many pounds of blueberries as pounds of strawberries and he made $225 altogether. Write a system of equations that could be used to determine the number of pounds of strawberries sold and the number of pounds of blueberries sold. What are two systems of equations?