If each side of an equilateral triangle is halved, its area will be :

1. halved

2. four times

3. unaltered

4. one-fourth

The area of a triangle is 37.5 cm². If its base is 12.5 cm; the corresponding altitude is :

1. 3 cm

2. 25 cm

3. 6 cm

4. 12 cm

The sides of a triangle are 9 cm, 12 cm and 15 cm; the area of the triangle is :

1. 54 cm²

2. 96 cm²

3. 108 cm²

4. 135 cm²

Find the area of a triangle whose sides are 18 cm, 24 cm and 30 cm.

Also, find the length of altitude corresponding to the largest side of the triangle.