I attached the diagram below. By the way, the triangle is AMN not ABC

Note that the altitude of an equilateral triangle bisects one of it's angles and divides the base it hits in two equal parts. This means that

Also, since is equilateral,

We are told that the sum of AM and MH gives 11m - 4

The side length of the triangle is equal to the side-length of AN

So, the side-length is 7m - 1 = 7(5) - 1 = 34