Kasur pegas (spring bed) berukuran panjang 2 m, lebar 1,8 m, dan tinggi 0,4 m. Hitunglah luas kain yang dibutuhkan untuk menyarungi kasur pegas tersebut!

<p>Jawaban yang benar adalah 6,64 m² &nbsp;&nbsp;</p><p>&nbsp;</p><p>Pembahasan</p><p>Luas kain untuk menyarungi kasur pegas artinya mencari luas permukaan balok tanpa alas karena bagian bawah kasur tidak menggunakan sarung kasur</p><p>Rumus luas permukaan balok</p><p>L = 2 x (pl + pt + lt)</p><p>&nbsp;</p><p>Luas permukaan balok tanpa alas yaitu luas permukaan balok - luas alas</p><p>LP balok tanpa alas = {2 x (pl + pt + lt)} - pl</p><p>Maka</p><p>LP balok tanpa alas = {2 x (pl + pt + lt)} - pl</p><p>&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp;={2 x ((2)(1,8) + (2)(0,4) + (1,8)(0,4))} - (2)(1,8)</p><p>&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp;= {2 x (3,6 + 0,8 + 0,72)} - 3,6</p><p>&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp;= {2 x 5,12} - 3,6</p><p>&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp;= 10,24 - 3,6</p><p>&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp;= 6,64</p><p>&nbsp;</p><p>Jadi luas kain yang dibutuhkan adalah 6,64 m² &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp;</p>