Two ropes are attached to a tree, and forces of F1 = 4i + 8j N and F2 = 3i + 6j N are applied. The forces are coplanar (in the same plane). What is the resultant force when F1 and F2 are added together?
a) 7i + 14j N
b) 1i + 2j N
c) 5i + 10j N
d) 9i + 18j N