What algebraic expression could represent the average of 2x, x + 3, and 6x?

Solve the given system of equations. 2y= -x+9 , 3x-6= -15

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)

What three-dimensional solid have 6 rectangular faces, 2 equal bases that are not rectangles and 18 edges