6h + (-8.7d) - 17 + 6d - 2.4h simplify the expression

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)

Find the solution of each of the following.

Find the value of x. round the length to the nearest tenth