Coloring 2 blocks of 100 squares and 7 units, each one corresponding to 0.01.
1) The difference between 3.31 -1.24 can be found by simply subtracting it.
3.31
-1.24
---------
2.07
2) Using base ten blocks, considering that the whole block is equivalent to 1 unit and each square is 0.01
Then we could sketch it 2.07, then we'd need two blocks to make it and 7 squares (each one corresponding to 0.01 of a unit.
Rounding off to the nearest unit, 2.07 or 207 squares which one corresponding 0.01, as the result of that difference between
3 blocks and 31 squares minus 1 block and 24 squares.