Answer:
 $7800
Step-by-step explanation:
The total interest earned can be found by summing the earnings from each of the investments.
Let x represent the total amount invested. Then Jessica's earnings are ...
 (x/2)(0.07) +(x/2)(0.13) = 780
Simplifying the equation gives ...
 (x/2)(0.07 +0.13) = 780
 0.10x = 780
 x = 7800 . . . . . . . . divide by 0.10
Jessica has $7800 invested.