An equilateral triangle has an altitude of 15 m. what is the perimeter of the triangle?

Equilateral triangle mean every sides and angles are equal 
so the measure of angles is 60 degrees 
 given that has an altitude of 15 m so this mean that 

sin 60 = altitude / hypotenuse 

sqrt3 /2 = 15/hyp.

hyp. = 15/(sqrt3 /2)

hyp. = 30/sqrt3 = 30sqrt3 / 3 = 10sqrt3

so in this way ve got that a side length is equal 10sqrt3 and the perimeter 

P = 3*10sqrt3 

P = 30sqrt3 m  so the 3rd choice is right,correct sure 

hope helped 

we know that

In the equilateral triangle every sides and angles are equal 

so

the measure of internal angles is equal to degrees 

see the attached picture to better understand the problem

In the right triangle ABC

where

BC is the altitude (opposite side angle degrees

AB is the hypotenuse

Clear AB

Perimeter of the triangle is equal to

but remember that

so

therefore

the answer is

84,864
multiply 221 by 384