Let the thickness of the box be tcm. Using the above concept, internal surface area A1=2[(12−2t)(10−2t)+(10−2t)(8−2t)+(12−2t)(8−2t)] According to the question, Ai=376 ⇒2[(12−2t)(10−2t)+(10−2t)(8−2t)+(12−2t)(8−2t)]=376 ⇒8[(t2−11t+30)+(t2−10t+24)+(t2−9t+20)]=376 ⇒3t2−30t+74=47 ⇒3t2−30t+27=0 ⇒t2−10t+9=0 ⇒t2−9t−t+9=0 ⇒t(t−9)−1(t−9)=0 ⇒(t−9)(t−1)=0 ⇒t=9 or 1