Find the length of an altitude of each triangle. me get the answers for 9-12

Method 1: Equilateral triangles (also are equiangular - each angle 60 degrees) have all sides the same length... and an altitude from a vertex will bisect (cut in half) the side it intersects. Also, a 2 congruent right triangles are formed.
 9. 4 ft = side length (this will be the hypotenuse when the altitude drops)
     2 ft = one of the legs in the new right triangle

a² + 2² =  4²
a² + 4 = 16
a² = 12
a = ×ft

Method 2: Using the information about 30 - 60 - 90 right triangle
The side opposite the 30 degree angle is half of the hypotenuse and the side opposite the 60 degree angle is the side opposite the 30 angle × .  The altitude is the side opposite the 60 degree angle...

10. altitude = (given side length of equilateral triangle)
altitude = m

11. altitude = =yd

12. If the perimeter is 24 units then a side is 24 units/3 = 8 units.
      altitude =  units