3. (15 points) A 20kg block of ice that is sitting on the surface of a frozen lake is being pulled by two people (Anna and Elsa) using ropes. (Assume there is no friction.) Anna is pulling the block to the north with a force of 70N. Elsa is pulling the block with a force that has a magnitude of 90N. The direction of Elsa's pull is towards 60 degrees to the south of east. a. What is the magnitude of the block's acceleration? b. If the block begins at rest, in which direction will it start moving?