42 if you multiply 6 and 7 it's 42 and multiply 21 and 2 and it will be 42 so that's the common denominator
Answer is A, you should not do negatives on the other side, copy the same monomial on the other sides
Try this option:
1. the sides of the biggest triangle are 16; x and √(16²-x²); the sides of the smallest triange are x;5 and y. The smallest triangle ~ the biggest triangle. Using the property of the similar triangles:

2. according to the Pyphagorean theorem (in the smallest triangle):

answer: y=√55.
3 7 is the answer I hope this helps