Point k is the midpoint of line segment jl, and kl=4. how do u find jk

Can someone pls ! pls answer all. no explanation needed..

David is spreading mulch on a triangular area of his flower bed. the coordinates of the vertices of the area are (1, 3), (9, 3), and (4, 6). what is the area of the triangle if each square has an area of 3 square feet?

What is the value of n in the equation -1/2(2n+4)+6=-9+4(2n+1)