1. What is the perimeter of a rhombus?

The perimeter of a rhombus is four times the length of its side. (A rhombus has four equal sides.)

2. Which units are used to measure perimeters?

The units for the perimeter of a shape are the same as the unit for the sides of the shape. i.e. Units of length

3. What has to be done if one measurement is in one unit and the other in a different unit?

Before adding the lengths, both measurements must be in the same units.
e.g. If the length of a rectangle is given as 3m and the width as 75 cm, one way would be to change 3m into 300 cm.
Then the perimeter can be found by calculating 2 x 300 + 2 x 75 which equals 750 cm which is equivalent to 7.5 metres.