Thank you for the opportunity to help you with your question!

Thank you for the opportunity to help you with your question!

As 15N is the net force therefore using Newton's law we have

Force=mass*acceleration

15=12*a

a=1.25m/s^2

Given the body starts from rest,initial velocity=0

To calculate the final velocity of the body.Let the final velocity be v

Using the equation

v=u+at,

v=final velocity=to calculate

u=initial velocity=0,as the body starts from rest

a=acceleration=1.25m/s^2,calculated above.

t= time taken =6 second

v=0+1.25*6

v=7.5m/s(answer)

Please let me know if you need any clarification. I'm always happy to answer your questions.Please let me know if you need any clarification. I'm always happy to answer your questions.