<span> 2ab + 2bc + 2ac the formula for the rectangular prism and i'm guessing you would find the answer to this than you would find your formula for the cube which is </span><span><span>6 a </span>2 and you would find that answer. </span>You would take your total for the rectangular prism answer and subtract the cube answer from it and you would probably get your answer. hope that helped?! :)
