Add.
4 5/7 + 3 3/4 =
my answer is 7 41/ is this correct ?

In order to find the correct answer you need to have the same denominator.  Change them to improper fractions:
4 5/7= 33/7
3 3/4= 15/4
To get the same denominator find the lcm.
You were right with that, 28.
To even this out multiply 33 by 4, 132.  132/28
15*7= 105.  105/28
132/28 + 105/28 = 237/28
237 divided by 28 = 8 13/28

C=2*pi*r C=37.69911 or 37.70