Three different electric charges q 1 ,q 2 , and q 3
​
exert forces on a test charge Q. The forces are, respectively, F1=(7,1), F2=(−3,5), and F3=(9,−8). The net force, F
net , is given by F net
​
= F
1​
+ F 2​​
+ F 3
​​
(a) Find F
net F
net
ne
​
=(, (b) If a fourth charge, q 4
​
, is added, what force F
must it exert on Q so that Q feels no net force at all, that is F net ​
=0 ? F
4
​=()