tolong bantuin ya pliss

Luas permukaan balok = 2 × (p×l) + (p×t) + (l×t)
= 2 × ( 21×14 ) + ( 21×16 ) + ( 14×16 )
= 2 × ( 294 + 336 + 224 )
= 2 × 854 = 1.708