Brainliest plus points
hint- answer to a is 0.84 metre squared
answer to b is 0.072 metre cubed
i just need full working out ; )

Step-by-step explanation:

a)  Internal surface area:

height h = 300 mm = 3 cm =0.3 m

breadth  b = 1000 -(300+300) = 1000 - 600 = 400 mm = 0.4 m

length l = 1200 -  (300+300)   = 1200 - 600 = 600 mm = 0.6 m

Internal surface Area = lb + 2hl + 2bh

                                   = 0.6 * 0.4  + 2 * 0.3 * 0.6  + 2 * 0.4 * 0.3

                                    =  0.24 + 0.36 + 0.24

                                      = 0.84 sq.m

b) Volume

volume = lbh

             = 0.6 * 0.4 * 0.3

              = 0.072 cu. m