The sum of 8 times a number and 7.....sum means add
8n + 7
is twice the number...is means equals
= 2n
so we have : 8n + 7 = 2n
The circumference of the circle formula is 2πr or πd.
We will use πd since we know the diameter.
C = πd
C = (3.14)(16)
C = 50.24
Hope this helps :)