2 pounds.
60(20) = 1200 = area
If 300 square feet requires 1/2 pound, you can divide 1200 square feet by 300 square feet.
1200/300=4
4 times 1/2
4(1/2)=2
For every 300 square feet, you need half a pound. If you were to have 600 square feet, you would need a pound of grass seed. Therefore, for 1200 square feet, you need 2 pounds of grass seed.