So if Beth ran the 400 meter dash in 57.2 seconds, and that time was 2.4 seconds faster than her previous time, she would have run a 59.6 second previous time. The equation would be X (current time) + Y (time difference) = Z (Previous time) we can see that her current time is 57.2 seconds, so that would replace X. We now have 57.2+Y=Z. So we can see in the problem that it was 2.4 seconds faster, so that’s the time difference. Our new equation is 57.2+2.4=Z. Now all we have to do is add 57.2 and 2.4 and you get her previous time, which is 59.6 seconds. Hope this helped! :D