So if the shapes are similar, they have to have a number multiple from to get the other triangle. If you divide 63 by 42, you get 1.5. Then you have to divide 54 by 1.5 to get G and that would be 36.
Answer is choice B: the circumference of a circle is the same as perimeter and is defined by πd (or pi times diameter) We can cut this in half because we are working with a semicircle: so we have 6π which approximates to the value in answer
when using 3.14 for pi
Woops: forgot to add the diameter of 12 so we would have 30.84