Solve: 2(2 x + 9) = 5 x + 72 which step is wrongstep 1: 4 x + 18 = 5 x + 72 step 2: 9 x + 18 = 72 step 3: 9 x = 54 step 4: x = 6

Step 2 is wrong because they combined like terms incorrectly.  The equation should be:  18 = x + 72.  Then, in Step 3, you would get x = -54.

Step-by-step explanation:

The given equation is a multi-step equation involving the distributive property.  You would first complete the distributive property by multiplying each term inside the parenthesis by the outside term.  Step 1 of the problem completes this step correctly.  The next step in the problem would be to use inverse operations to combine like terms and isolate the variable - whatever you do to one side of the equation, you must do to the other.  In this case, we need to subtract 4x from both sides, not add, to get:  4x - 4x + 18 = 5x - 4x + 72.  This gives us 18 = x + 72.  To solve for x, we need to subtract both sides by 72:  18 - 72 = x + 72 - 72, or x = -54.