Answer:
0.15
Step-by-step explanation:
To fill the squares look for the one filled in column/row/diagonal and figure out its sum.
All other columns/rows/diagonals must be equal to that, so whenever there is a column/row/diagonal with a single missing value you can add the others up and calculate the missing value.
So you have to find those single missing value columns/rows/diagonals, fill them out and continue with the next one until the whole square is filled in.
20 can be divided by 2 twice, with 5 remaining
20 can be divided by 4 once, with 5 remaining
20 can be divided by 5 once, with 4 remaining
20 can be divided by 10 twice
20 can be divided by 20 once
hope this helps
The missing factor is (a -1) I believe. If you foil (5a + 9)(a - 1) you would get 5a^2 + 4a - 9.