Question 1004205
I spent a few minutes checking the drawing in your book and reading the brief instructions.  DRAW the altitude.  Doing so will give you two right triangles which share this altitude.  Keep working through and you may find expressions whose sum would be y.


Below is a precise description with some calculation, but not taken to completion.  You should be able to do so with very little trouble.


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Part  of the work...
Using the right triangle on the left side, let h be the height or altitude for BOTH triangles.  
{{{h/16=sin(30)}}}
{{{h=16*sin(30)}}}


The segment length y, the base for the triangle  (before or after making the altitude) is composed of two parts.  {{{y[1]}}} and {{{y[2]}}}; sub 1 for the part in the left right triangle, sub 2 for the one on the right.
There will be {{{y=y[1]+y[2]}}}.


Left side right triangle, according to pythagorean theorem formula,
{{{(y[1])^2+(16*sin(30))^2=16}}}


The right side right triangle, gives you {{{(y[2])^2+(16*sin(30))^2=24^2}}}.


What to do from here, solve the separate sub-parts for {{{y[1]}}} and {{{y[2]}}}, and sum them.  {{{y=y[1]+y[2]}}}