In step 2 multiply what is inside the parenthesis by 7 (distributive property): 
 7 * x = 7x 
 7 * 3 = 21 
 In step 3 subtract -7x on both sides of the equation. (Property of subtraction of equality)
 Then -7x + 4x = -3x 
 7x-7x + 21 = 21 
 In step 4, both sides of the equation are divided by -3. (owned by the equality division)
 So: 
 -3x / -3 = x 
 -21 / -3 = 7 
 Recall that the division of equal signs results in a positive number.