the swimmer had sped up 0.2 m/s cause that's the difference between 1.1 m/sec and 1.3 m/s.
Then, what you do is, you divide the amount increased by the time it takes to increase that much, so 0.2 / 20 = 0.01
the acceleration rate is 0.01 m/s per second. hope this helped!! ^-^
