*PLEASE HELP* When an object is placed in front
of a convex lens, it creates a virtual
image at -12.8 cm with a
magnification of 2.85. What is the
focal length of the lens?
(Mind your minus signs.)
(Unit = cm)

The focal length of the lens = 3.32 cm.

Explanation:

Lens formula :    (i)

f= focal length , v=image distance , u =object distance.

magnification: m =   (ii )

Given: v= -12.8 cm , m =2.85

Put values in (ii), we get

substitute values of u , v in (i)

Hence, the focal length of the lens = 3.32 cm.

when jerome paddle in flowing river towards east the net speed of jerome will increase

so the net speed of jerome will be given as

now the speed of paul will be same as it is given as he is running on the ground

so

so here we can say since the speed of jerome is more so he will win the race

now as we know the distance so the time difference is given as

so jerome will reach first and the time difference will be 203.55 s or 3.4 min