Answer:
3 more square feet.
Explanation:
x = The amount Melinda can shovel in 1 minute
y = The amount Paula can shovel in 1 minute
So make two equations:
30(x + y) = 450 x + y = 15 x = 15 - y
20x + 25y = 345 4x + 5y = 69
Plug in:
4(15 - y) + 5y = 69
60 - 4y + 5y = 69
y = 9
x = 6
9 - 6 = 3