Explanation:
HEY PLS DON'T JOIN THE ZOOM CALL OF A PERSON WHO'S ID IS 825 338 1513 (I'M NOT SAYING THE PASSWORD) HE IS A CHILD PREDATOR AND A PERV. HE HAS LOTS OF ACCOUNTS ON BRAINLY BUT HIS ZOOM NAME IS MYSTERIOUS MEN.. HE ASKS FOR GIRLS TO SHOW THEIR BODIES AND -------- PLEASE REPORT HIM IF YOU SEE A QUESTION LIKE THAT. WE NEED TO TAKE HIM DOWN!!! PLS COPY AND PASTE THIS TO OTHER COMMENT SECTIONS!!

1) x=9, because we can use the Pythagorean theorem, x^2 + 144 = 225, x^2 = 81
2)
, because 6^2 +6^2 = 72, 
3)
, because 
hope this helps... load for images!