The second line is the correct answer. 2+(-8)=10 because the parathese makes it positive so 2+8=10
I assume that the numbers are supposed to be written as 7.14 x 10^10 for December and 3.21 x 10^10. The total mail delivered is the sum of these two numbers.
(7.14 x 10^10) + (3.21 x 10^10) = 1.035 x 10^11
