First, to make things easier, let's turn 5/4 into a decimal given a second is equal to 1000 milliseconds.
5/4 = 1,25
1,25 * 1000 = 1250 milliseconds = 1.25 seconds
So, we've found that 45 yards can be covered in 1.25 seconds. Now we'll use the rule of 3:
45 - 1.25
80 - x
Now we solve:
(80 * 1.25) / 45 = x
100 / 45 = x
2,22... = x
So, according to our answer, 80 yards can be covered in 2,22 seconds, which in fractions would be:
Hope it helped,
BioTeacher101