The answer is D. for sure 21 square inches
Answer: Metal A is 3 times faster than Metal B.
Step-by-step explanation:
Since we have given that
Time taken to oxidised metal A = 
Time taken to oxidised metal B =
seconds
So, ratio of metal A to metal B would be

So, Ratio of Metal A to Metal B is 1 : 3.
Hence, Metal A is 3 times faster than Metal B.
90 degrees in a right angle.