You would do 4^2 - 2^2 = 16 - 4 = 12. The final answer is B) √12 units. This is because you're doing the reverse Pythagoras' theorem, so you still have to square root. I hope this helps!
what you do is.... 2^2+b^2=4^2... 2 squared is 4. leave b squared 4 squared is 16. so you have 4+b^2=16 subtract 4 on both sides to get 12. 12=b^2 *find the square root* the square root of 12 is 3.46 so therefore b=3.46
