mary is walking on the plane starting from the point (-1,5); she reaches the point (2,3) after 4 seconds and continues on. at the exact time mary crosses the y axis, bob is standing at the origin and starts running from the origin towards the point (6,6) at a speed of 3√2 units/sec. write a formula for the distance between mary and bob t seconds after mary starts moving (hint, use a multipart function).