First we look at the inner part: 

That asks for the angle between  and  whose sine
is .  

Since we know that ,
we draw such an angle by placing a right triangle
in the first quadrant whose angle at the origin is such that its
opposite side is y=1 and its hypotenuse is r=7, like this:



The angle indicated by the red arc is the angle: .

To find the tangent, we must calculate the adjacent side x,
using the Pythagorean theorem:









So we now have all three sides of the right triangle:



The problem is 



and since we know that 

.

Edwin

  is  .


So,  they want you calculate  ,  where  = .


Since   = ,  it means that   = .


Then   =  =  =  =  =  = .


Finally,    =  =  =  = .