Answer:
66 cm
Step-by-step explanation:
Diameter (d) = 21 cm

It's the points of the triangle E----------G
They are the twin points
I agree with Roaltyjess<span />
Sum of two integers with different signs is equal to 8.
There are several answers:
+12 and -4
+10 and -2
+11 and -3
ETC.