Answer:
D. 20
Step-by-step explanation:
By setting up a system of equations we can easily solve this problem. Let's denote Jane's working hours with x and Jack's working hours with y. Since they don't want to work more than 65 hours, the first equation is x+y=65. The second equation is 14x+7y=770. By solving this system of equation
{
�
+
�
=
65
14
�
+
7
�
=
770
{
14x+7y=770
x+y=65
, we find that y=20 hours, which is Jack's maximum working hours.