Question

What is the most efficient first step to isolate the variable term on one side of this equation? -9x = -4x + 5

A. Subtract 5 from both sides.
B. Add 5 to both sides.
C. Subtract 9x from both sides.
D. Add 4x to both sides.

Answer 1

D. Add 4x to both sides gets all of x on one side with the solution on the other side.

Answer 2

The most efficient 1st step to solve this equation is to add 4x to both sides of equation, then you get

$-9x+4x=-4x+4x+5,\\ \\-5x=5.$

This equation you can solve by dividing the whole equation by (-5):

$x=5:(-5),\\ \\x=-1.$

Answer: option D.