What is the formula to calculate the length of a diagonal of a rectangle?

If the area of a square is $2.5 {\mathrm{m}}^2$, then which of the following is equivalent to this area?

If the area of a square field is $289 {\mathrm{m}}^2$, then what is the length of its side in kilometers?

Find the number of bricks of size $20 \mathrm{cm}\times 15 \mathrm{cm}$ needed to cover the path of $45 \mathrm{m}\times 20 \mathrm{m}$?

If a rope of length $18 \mathrm{cm}$ is used to make an equilateral triangle, then find the space covered by the triangle. 

Find the area of a parallelogram with base $13 \mathrm{cm}$ and altitude $11.2 \mathrm{cm}$.

The length of a side and diagonal of a rhombus is $13 \mathrm{m}$ and $10 \mathrm{m}$ respectively. Find the area of the rhombus.