How many subsets of at least one element does a set of six elements have

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)

If a || b and e || f , what if the value of y ?

Find cot x if sin x cot x csc x = √2