You can put this solution on YOUR website!
LATERAL SURFACE OF A PRISM or LSA = perimeter of base * height
Since in your case prism is of rectangular base ...so
perimeter of base of prism = perimter of rectangle [i.e = 2(lenght+breath)]
also height is also given
so can you now find the LSA of rectangular prism...?
Still if you won't be able to solve further, contact me again.
hope this will help you
Please feel free to revert back for any further queries.