The three sides of the triangle are equal and thus this is an equalateral triangle with 3 of the same angles. Thus angle LNM and NML are the same!
we can now make an equation
7x-3 = 11y + 5
Hmm, but we have two unknowns :/
We know that all triangles must add up to 180o so with 3 angles we get each angle to 90o!
Thus we dont even need the first equation (unless we needed it for something else)
so 90 = 7x - 3
7x = 93
x = 13.29
