Part 1)
here Julie is running at speed 5 m/s
So here two balls are thrown at speed 10 m/s towards Julie with respect to her friend standing on the ground.
So here this all speed is real speed of all.
Now as per Anita (let say she is one of her friend standing on ground) the speed of two balls will be same as the given speed as she is observing from ground or stationary frame
As per the frame of Julie
speed of ball 1

towards her in same side
speed of ball 2

towards her from opposite side
Part b)
Now in this case the speed of two balls is given with respect to Julie
so we can say
for ball 1


so in ground frame speed of ball 1 is

Similarly for ball 2


So speed in ground frame of ball 2 is

so its 5 m/s from opposite side
If the force and the motion are along the same direction (like it is here) then work is force*distance. The time doesn't come into play until you want the power used. So here
W=9.0*3.0=27J