If two cubes are joined, then the resultant shape will be a cuboid and the length of that cuboid will be twice the edge of each cube,breadth and height are the edge of cube.
Therefore,the length of the cuboid(l)=2*5=10cm
Breadth of the cuboid(b)=5cm
Height of the cuboid(h)=5cm
Total surface area of the cuboid=2[lb+bh+lh]
Cost of painting=250(300)=Rs.75,000.
its cost is 30 rupees per meter square
But it is given 300 in the question
so take it 300 but it is metre square