An athlete swims the length L of a pool in a time t1 and makes the return trip to the starting position in a time t2. (a) If she is swimming initially in the positive x-direction, determine her average velocities symbolically in (a) the first half of the swim, (b) the second half of the swim, and (c) the round trip. (Assume that time t2 is from the other end of the pool to the starting point. Use any variable or symbol stated above as necessary. Indicate the direction with the sign of your answer.)