Radius is equal to 1/2 the diameter. The radius is 14 (28/2=14)
With your formula:
c=2*14
c=28
HOWEVER I believe you meant
c=2(pi)r
In which
c=2(pi)14
c=28(pi)
In this instance for pi we can use 3.14 since we will be rounding anyway, so
c=28*3.14
c=87.92
Rounded to be
c=88
Note:
If we didn’t round pi out to 3.14 we would have gotten 87.964594...
