Answer:
Step 4 is incorrect he did not divide correctly from step3 to step 4
Step-by-step explanation:
The circumference of a circle is
C = 2 * pi *r
We know the circumference is 12 pi
12pi = 2 pi *r
Divide each side by 2 pi
12 pi/2pi = 2pi r/ 2pi
6 = r
From step 3 The student did not cancel the pi in the top and the bottom on the right hand side to isolate r
In step 4 he got 6 =pi r instead of pi
The answer is 84 because 21 times 4 equals 84
