Answer:
√108
Step-by-step explanation:
a^2+b^2=c^2
so the longest side is c
1. and it doesn't matter which is A or which is B as long as C is the longest side. than you put it in 6^2+b^2=12^2
2. 36+b^2=144
3. -36 on both sides b^2=108 and to take off the b^2, make it √108. and done
