Write three sets of Pythagorean triplets such that each set has numbers less than 30.

A Pythagorean triplet has one number equal to 6. The Pythagorean triplet are :

1. 5, 6, 7

2. 6, 7, 8

3. 4, 6, 8

4. 6, 8, 10

The greatest 3-digit perfect square number is :

1. 121

2. 961

3. 100

4. 900

The area of a square plot is 441 m². Its perimeter is :

1. 84 m²

2. 84 m

3. 21 m

4. 21 m²