Divide 3 apples by $2.50 to get the unit price, $1.20 (The constant of proportionality)
Then multiply 12 apples by the constant ($1.20)
Your final answer should be $14.40
1) given 6x = 4x + 140
2) subtract 4x from both sides => 6x - 4x = 4x - 4x + 140
=> 2x = 140
3) divide both members by 2 => 2x / 2 = 140 / 2
=> x = 70
4) Answer: x = 70