It is required that the product is of positive sign i.e it is 35.28

So we multiply -8.4 x -4.2 (we cannot chose 1.3 as 8.4 x 1.3 will be close to 10 or 11 and not near enough to 35.28)(we cannot multiply one negative number and one positive number and get a positive number so 7.3 is ruled out)