The number is 4,500.00
From the decimal point, moving to the left, the place values would be ONES, TENS, HUNDREDS, THOUSANDS, TENS THOUSAND, HUNDREDS THOUSANDS.
Since Darcy placed 4 in the thousands blocks, it should look like this 4,000.
Then 5 should be in the hundred block; thus, 500.
Adding both numbers resulted to 4,500. Four thousand five hundred only.