Kevin had 13 coins in his pocket. all of his coins are either dimes or quarters. when he emptied his pocket, kevin found that he had $2.05. how many dimes and quarters does he 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)