+6 -3 0 +15 -1 +8 +11 -6​

How to do this , and can some one explain

Atriangle has a side lengths of 18cm, 80 cm and 81cm. classify it as acute obtuse or right?

How do i start to solve? would appreciate a walk-thru! a bird sitting 16ft above the ground in an apple tree dislodges an apple. after how many seconds does the apple land on the ground? (assuming that no branches will interfere with it's fall)