The floor of a building consists of 3000 tiles which are rhombus shaped and each of its diagonals are 45 cm and 30 cm in length.

Given:

The floor consist of 3000 rhombus shaped tiles.

The lengths of the diagonals of each tile are $45 \mathrm{~cm}$ and $30 \mathrm{~cm}$.

$\therefore$ Area of a rhombus shaped tile $=\frac{1}{2} \times(45 \times 30)=675 \mathrm{~cm}^{2}$

$\therefore$ Area of the complete floor $=3000 \times 675=2025000 \mathrm{~cm}^{2}$

Now, we need to convert this area into $\mathrm{m}^{2}$ because the rate of polishing is given as per $\mathrm{m}^{2}$.

$\therefore 2025000 \mathrm{~cm}^{2}=2025000 \times \mathrm{cm} \times \mathrm{cm}$

$=2025000 \times \frac{1}{100} \mathrm{~m} \times \frac{1}{100} \mathrm{~m}$

$=202.5 \mathrm{~m}^{2}$

Now, the cost of polishing $1 \mathrm{~m}^{2}$ is Rs 4 .

$\therefore$ Total cost of polishing the complete floor $=202.5 \times 4=810$

Thus, the total cost of polishing the floor is Rs 810 .