Over a three month period a pet food store receives 1770 lbs dog food, 1165 lbs cat food, and 365 lbs of birdseed. first shipment was 60% dog food, 25% cat food, and 15% bird seed, second shipment was 50% dog food, 35% cat food, and 15% bird seed, third shipment was 50% dog food, 45% cat food, and 5% bird seed. write a system of equations to find the number of lbs of pet food in each of the three shipments.