Imagine 3/4 of a mile as
a mile cut in 4 parts and
Adrian jogs only 3 of the 4 parts in a day so one of the 4 parts is not ran
In 3 days he will have 3 of the 1/4 parts not ran that he can ran it the next day
3/4+ 3/4+3/4+3/4= 3+3+3+3/4=
12/4=3 miles in 4 days
You can also write as
3miles/ ( 3/4)= (3/1)•(4/3)= 3•4/1•3=12/3=
4 days